Bulletin  154 


December,  1919 


UNIVERSITY  OF  FLORIDA 


Agricultural  Experiment  Station 


CITRUS  FERTILIZER  EXPERIMENTS 


By 
S.  E.  COLLISON 


The  Station  Bulletins  will  be  sent  free  upon  application  to  the  Experiment 

Station,   Gainesville 


BOARD  OF  CONTROL 

J.  B.  Hodges,  Chairman,  Lake  City,  Fla. 

E.  L,  Wartmann,  Citra,  Fla. 

J.  B.  Sutton,  Tampa,  Fla. 

J.  T.  Diamond,*  Tallahassee,  Fla. 

H.  B.  Minium,  Jacksonville,  Fla. 

Bryan  Mack,  Secretary,  Tallahassee,  Fla. 

J.  G.  Kellum,  Auditor,  Tallahassee,  Fla. 


•Resigned. 


CITRUS  FERTILIZER  EXPERIMENTS      /,  IT 

By  S.  E.  COLLISON  ■     ^ 

The  judicious  use  of  commercial  fertilizers  in  the  orange  grove 
has  been  one  of  the  important  problems  confronting  the  Florida 
citrus  grower.  In  the  expense  involved  and  the  effects  upon  the 
tree  and  fruit,  this  problem  ranks  as  of  equal  importance  with 
any  of  the  other  operations  in  the  grove,  such  as  spraying,  har- 
vesting, pruning  or  cultivation.  At  the  time  when  the  work  re- 
ported in  this  bulletin  was  begun,  practically  no  experimental 
work  in  this  line  had  been  carried  out  in  the  state.  The  existing 
knowledge  of  the  effects  of  the  various  fertilizers  in  use  was 
entirely  the  result  of  the  practical  experience  of  the  growers 
themselves  and  was  of  a  more  or  less  conflicting  nature.  In  order 
to  obtain  accurate  knowledge  of  the  effects  of  various  fertilizers 
over  a  comparatively  long  period,  the  experimental  work  dis- 
cussed in  this  bulletin  was  undertaken.  A  young  grove  was 
located  on  Lake  Harris,  about  three  miles  from  Tavares,  in  Lake 
county,  and  used  for  the  experiment.  The  piece  of  land  was 
selected  with  special  reference  to  protection  from  cold,  adapta- 
bility to  citrus  culture  and  uniformity  of  type  of  soil.  It  is  gen- 
erally considered  that  the  influence  of  the  fertilizer  treatment 
given  citrus  trees  may  extend  over  a  period  of  several  years  after 
that  particular  treatment  has  been  discontinued.  In  order  to  elim- 
inate this  disturbing  factor  from  the  experiment  it  was  deemed 
advisable  to  begin  with  young  trees.  Accordingly,  one  year  old 
budded  trees,  all  of  the  same  variety,  especially  selected  with 
regard  to  uniformity  of  size,  and  all  from  the  same  nursery, 
were  used  in  the  work.  They  were  set  out  in  January,  1900,  three- 
quarters  of  a  pound  of  bone  meal  being  given  each  tree. 

OBJE(  TS  OF  THE  EXPERIMENT 

The  objects  of  the  experiment  were  to  determine  the  effects 
of  various  fertilizers  upon  the  chemical  composition  of  the  soil, 
upon  the  growth  and  composition  of  the  trees  and  upon  the  fruit. 
The  effects  of  lime  and  other  alkaline  materials,  and  of  various 
cultural  treatments  upon  the  soil  and  upon  the  trees  were  also 
objects  of  study.  To  supplement  the  work  in  the  grove  with 
fertilizers,  a  number  of  soil  tanks  were  made  use  of  on  the  horti- 
cultural grounds  of  the  p]xi)eriment  Station. 

PLAN  OF  EXPERIMENT 

The  grove  was  divided  into  48  plots  of  ten  trees  each.  Those 
trees  were  Valencia  Late  on  sour  stock,  and  were  set  lo  bv  .30 


2\<n  S5 


Florida  Agricultural  Experiment  Station 


•g*           '/fc'           'ZV'          'Si'           'V^'           •yS'' 

Fig.   1. — Diagram  of  plots   in  the  ten  year  fertilizer  experiment 

TABLE  1. — Fertilizer  Mixtures  Used 

An  application  of  two  pounds  per  tree  was  taken  as  the  standard  amount. 

(  Ammonia,  5  per  cent.,  from  sulphate  of  ammonia. 
Standard    formula  J  Phosphoric  acid,  6  per  cent.,  from  acid  phosphate, 
(for  young  trees)    J  Potash,    6   per   cent.,   from    high-grade    sulphate    of 
'      potash. 


Bulletin  154,  Citrus  Fertilizer  Experiments  5 

Variations  from  the  Standard 
Half  the  standard. 
Standard. 

Double  the  standard. 
Four  times  the  standard. 

Phosphoric  acid  and  ammonia  increased  by  one  half. 
Phosphoric  acid  and  potash  increased  by  one  half. 
Ammonia  and  potash  increased  by  one  half. 
Phosphoric  acid  and  potash  decreased  by  one  half. 
Phosphoric  acid  and  ammonia  decreased  by  one  half. 
Ammonia   and   potash   decreased   by   one   half. 
Standard  and   finely   ground   limestone. 
Standard  and  air-slaked  lime. 
Standard  and  mulch. 
Standard. 

Sources   of  Nitrogen 
From  nitrate  of  soda. 

Half  from  nitrate  of  soda,  and  half  from  sulphate  of  ammonia. 
From  dried  blood. 

Half  from  sulphate  of  ammonia,  and  half  from  dried  blood. 
Half  from  nitrate  of  soda,  and  half  from  dried  blood. 
From  cottonseed  meal. 

From  cottonseed  meal.    (With  ground  limestone.) 
Half  from  cottonseed  meal,  and  half  from  sulphate  of  ammonia. 
Half  from  cottonseed  meal,  and  half  from  nitrate  of  soda. 

Sources  of  Phosphoric  Acid 
From  dissolved  boneblack. 
From  steamed  bone. 
From  steamed  bone.    (Double  amount.) 
From  Thomas'  slag.    (Nitrogen  from  nitrate  of  soda.) 
From  Thomas'  slag.    (Double  amount.    Nitrogen  from  nitrate  of 
soda.) 
Plot  29.     From    acid   phosphate.     (Potash,   7%    per   cent,   in   June,   7%    in 

October,  and  3  in  February.) 
Plot  30.     From  acid  phosphate.     (Nitrogen  from  nitrate  of  soda.     Potash 

from  hardwood  ashes.) 
Plot  31.     From  acid  phosphate.    (Standard.) 
Plot  32.     From  dissolved  boneblack. 
Plot  33.     From  floats. 
Plot  34,     From  floats.    (Double  amount.) 
Plot  35.     From  floats.    (Four  times  amount.) 

Plot  36.     From    floats.     (Four    times    amount.     Nitrogen    from    cottonseed 
meal.) 

Sources   of   Potash 

Plot  37.  From  low-grade  sulphate. 

Plot  38.  From  muriate. 

Plot  39.  From  high-grade  sulphate  of  potash.    (With  ground  limestone.) 

Plot  40.  From   kainit. 

Plot  41.  From  high-grade  sulphate  of  potash.    (Standard.) 

Plot  42.  From   nitrate   of  potash.     (Balance  of  nitrogen  from   nitrate   of 
soda.) 

Variations  from   the   Standard 

Plot  43.  No  fertilizer. 

Plot  44.  Standard. 

Plot  45.  Standard  and  mulch. 

Plot  46.  Standard  and  clean  culture. 

Plot  47.  Nitrogen  from  dried  blood.     Clean  culture. 

Plot  48.  Nitrogen  from  nitrate  of  soda.     Clean  culture. 


Plot 

1. 

Plot 

2, 

Plot 

3. 

Plot 

4, 

Plot 

5. 

Plot 

6. 

Plot 

7. 

Plot 

8. 

Plot 

9. 

Plot 

10. 

Plot 

11. 

Plot 

12. 

Plot 

13. 

Plot 

14. 

Plot 

15. 

Plot 

16. 

Plot 

17. 

Plot 

18. 

Plot 

19. 

Plot 

20. 

Plot  21. 

Plot  22. 

Plot 

23. 

Plot 

24. 

Plot  25. 

Plot 

26. 

Plot  27. 

Plot  28. 

6 


Florida  Agricultural  Experiment  Station 


feet.  The  diagram  in  Figure  1  shows  the  relation  of  the  plots  to 
each  other.  The  fertilizer  and  other  treatment  given  these  forty- 
eight  plots  is  shown  in  Table  1.  A  standard  formula  consisting 
of  5  percent  ammonia,  6  percent  phosphoric  acid,  and  6  percent 
potash,  was  used.  In  the  fall  this  was  changed  to  21/2  percent 
ammonia  and  8  percent  potash,  the  phosphoric  acid  remaining 
the  same.  The  standard  mixture  consisted  of  sulphate  of  am- 
monia, acid  phosphate,  and  high  grade  sulphate  of  potatsh.  As 
shown  in  Table  1  this  mixture  was  varied  for  different  plots  by 
substituting  other  sources  of  the  three  essential  elements  for 
those  in  the  standard  mixture.  The  standard  mixture  was  used 
at  first  at  the  rate  of  2  pounds  per  tree  three  times  a  year.  This 
amount  was  gradually  increased  so  that  at  the  end  of  the  experi- 
ment the  "standard"  plots  were  receiving  an  application  of  six 
pounds  instead  of  two. 


TABLE  2. — Composition  of  Grove  Soil.   Analysis  of  Composite  Sample 


Soil 

Subsoil 

Insoluble  matter 

94.09 
2.55 
.033 
.10 
.047 
.134 
.13 
.14 
.10 
.98 
2.30 
trace 
none 

94.81 

Volatile  matter 

1.71 

Nitrogen    

.018 

Phosphoric  acid                                           

.09 

Potash    

.025 

Soda    

.115 

Lime   

.17 

Magnesia   

.09 

Manganese  oxide  

.14 

Ferric   oxide   

.96 

Aluminum    oxide   

2.40 

Sulphur   trioxide   

trace 

Carbon  dioxide  

none 

P205 

N 

1st  foot  

.12 
.10 
.09 
.09 
.09 

.030 

2nd  foot  

.015 

3rd  foot .            

.013 

4th  foot  

.012 

5th  foot  

.009 

Plots  46,  47  and  48  were  cultivated  during  the  entire  year. 
Plots  13  and  45  were  mulched  with  a  mixture  of  forest  leaves, 
grass,  etc.  The  remainder  of  the  grove  was  cultivated  up  to 
the  rainy  season  (about  June  1),  and  then  a  cover  crop  allowed 
to  occupy  the  land  until  in  September,  when  it  was  either  turned 
under  or  cut  for  hay  and  the  stubble  plowed  under.  During  the 
early  years  of  the  experiment  this  cover  crop  consisted  of  beg- 
garweed.  The  soil  finally  became  too  acid  to  support  a  good  crop 
of  the  beggarweed,  and  was  at  first  supplemented  with  cowpeas, 
and  later  on  with  velvet  beans. 


Bulletin  154,  Citrus  Fertilizer  Experiments 


TABLE  3. — Nitrogen 

AND  Phosphoric  Acid  in 

Soil 

A 

B 

C 

D 

E 

F 

G 

Ave. 

N 
P205 

.029 
.09 

.040 
.12 

.033 
.08 

.033 
.11 

.037 
.12 

.030 
.10 

.028 
.09 

.033 
.10 

Subsoil 

N 
P205 

.018         .018 
.09            .12 

.015         .020         .019         .018 
.08           .09           .11            .08 

.016 
.08 

.018 
.09 

The  effects  of  the  various  treatments  on  the  trees  were  meas- 
ured by  taking  at  regular  intervals  the  diameter  of  the  trunks 
six  inches  above  the  bud.  Notes  on  the  size,  general  appearance 
and  character  of  growth  of  the  trees  were  taken  from  time  to 
time. 

COMPOSITION  OF  SOIL 

The  soil  on  which  the  grove  is  located  is  a  rather  coarse  reddish 
sand  of  the  hammock  type,  verging  on  high  pine,  and  rather 
dry  in  character.  At  the  time  that  the  trees  were  set  out  com- 
posite samples  of  the  soil  (0-9  inches)  and  of  the  sub-soil  (9-21 
inches)  were  taken  and  analyzed.  In  one  place  in  the  field 
samples  of  the  first  five  feet  were  taken  and  the  phosphoric 
acid  and  nitrogen  contained  in  the  samples  were  determined. 
These  analyses  are  given  in  Table  2.  Samples  of  the  soil  and 
subsoil  were  also  taken  in  seven  different  places  in  the  field  and 
analyzed  for  phosphoric  acid  and  nitrogen.  These  analyses  are 
given  in  Table  3.  They  show  that  the  soil  over  the  field  was  of 
a  fairly  uniform  composition.  The  analyses  of  this  soil  as  a 
whole  indicate  that  it  is  somewhat  above  the  average  in  fertility 
as  compared  with  citrus  soils  in  general. 


Fijr.  2. — Sectional   view  of  tai.ks 


Florida  Agricultural  Experiment  Station 


Fig.  3. — Ground  plan  of  tanks 


LEACHING  OF  FERTILIZER 

In  order  to  supplement  the  work  with  fertilizer  in  the  field, 
soil  tank  experiments  were  begun  on  the  Station  grounds. 
By  this  means  it  has  been  possible  to  more  closely  measure  and 
control  conditions  than  where  the  work  has  been  conducted  on 
the  scale  necessary  in  field  experiments.  Accurate  estimates 
of  the  losses  of  fertilizing  materials  in  the  drainage  water  under 
different  systems  of  fertilizing  and  the  effect  of  long  continued 
use  of  fertilizers  on  the  soil  have  been  possible.  In  this  way  much 
interesting  light  has  been  thrown  upon  the  question  of  the 
capacity  of  the  average  sandy  Florida  soil  for  retaining  the 
fertilizing  ingredients  added  to  it  and  which  of  these  materials 
are  most  subject  to  leaching. 

Figures  2  and  3  illustrate  the  equipment  used  in  the  work. 
The  tanks  were  constructed  of  heavy  galvanized  iron,  painted 


Bulletin  15 U,  Citrus  Fertilizer  Experiments  9 

inside  and  out  with  a  chemically-resistant  paint.  Each  tank  had 
an  inside  diameter  of  5  feet  3Vi.  inches,  with  a  maximum  depth 
of  41/^  feet,  and  a  surface  area  of  one  two-thousandths  of  an 
acre.  As  shown  in  the  diagram,  the  bottom  of  the  tank  slopes 
to  one  side,  where  there  is  a  strainer  opening  into  a  two  inch 
tin-lined  iron  drainage  pipe,  the  length  of  which  is  a  little  over 
4  feet.  Four  such  tanks  open  into  a  central  collecting  pit  as 
shown  in  Figure  3.  Under  the  ends  of  the  drainage  pipes 
entering  at  the  four  corners  of  the  pit  were  placed  large  gal- 
vanized cans  for  collecting  the  drainage  waters.  These  cans 
were  coated  on  the  inside  with  paraffine  to  prevent  any  chemical 
action  of  the  drainage  water  upon  the  metal.  The  collecting  pit, 
which  is  about  8  feet  deep  and  6  feet  square  inside,  is  built  of 
brick,  with  a  concrete  bottom,  and  is  covered.  The  soil  tanks 
were  sunk  in  the  ground  to  within  a  few  inches  of  the  tops  and 
were  filled  with  soil  to  within  3  inches  of  the  rims.  The  soil 
used  was  a  rather  coarse,  gray  sand  of  high  hammock  type.  It 
is  described  'by  the  Bureau  of  Soils  as  Norfolk  sand.  In  filling 
the  tanks  a  layer  of  quartz  pebbles  was  first  placed  over  the 
sloping  part  of  the  bottom  in  order  to  provide  adequate  drainage 
and  to  prevent  the  soil  from  sifting  thru  the  strainer  and  filling 
the  drainage  pipe.  Above  the  layer  of  pebbles  was  placed  45 
inches  of  soil.  In  excavating  for  the  tanks  the  soil  was  removed 
in  layers.  First  a  9  inch  layer  was  removed  and  placed  at  one 
side  by  itself.  Then  the  soil  was  removed  in  one  foot  layers,  each 
foot  being  kept  separate  from  the  remainder.  The  last  foot  of 
excavated  soil  was  placed  in  the  bottom  of  the  tank,  then  the 
remaining  sections  ending  with  the  top  9  inches.  Thus  the 
soil  rested  in  the  tank  as  it  was  in  the  original  state.  Each  layer 
of  soil  was  well  packed  as  it  was  placed  in  the  tank,  the  same 
weight  of  dry  soil,  8,625  pounds,  being  used  in  each.  The  tanks 
were  then  exposed  to  natural  conditions,  the  drainage  water 
leaching  thru  the  soil  being  collected  from  time  to  time  as  it 
became  necessary,  and  analyzed.  This  treatment  was  continued 
for  a  period  of  10  months  during  which  time  the  soil  received  no 
fertilizer,  the  results  obtained  representing  the  losses  of  plant 
food  from  a  bare,  unfertilized  soil.  The  results  show  that  by  far 
the  greatest  loss  of  plant  food  falls  on  the  nitrogen  of  the  soil. 
The  thoro  aeration  which  the  soil  received  when  the  tanks  were 
filled  would  lead  to  more  rapid  nitrification  of  the  soil  organic 
matter  and  thus  to  somewhat  larger  losses  of  nitrogen  in  the 
drainage  water  at  first,  than  would  occur  under  natural  condi- 


10 


Florida  Agricultural  Experiment  Station 


TABLE  4 

— Loss  OF  Nitrogen  from 

Soil  Tanks 

V 

5:5 

Sulphate  of 
Ammonia 

Nitrate  of 
Soda 

Dried  Blood 

.1 

II 

m 

o 

*S 

CO 

.s 

CO 

09 

§  g 

(2Z 

CO 

0 

.s 

15 

July  13 
Aug.  23 
Sept.  5 
Nov.  22 
Jan.   8 

74.74 

.63 
1.18 
4.66 
8.46 
8.12 
5.72 
3.91 
10.14 
9.64 
6.43 
3.19 
.65 
1.61 

74.11 

72.93 

68.27 

78.49 

70.36 

64.64 

98.09 

87.95 

115.68 

109.25 

124.75 

161.46 

159.85 

197.23 

213.38 

211.66 

211.09 

210.50 

247.08 

282.12 

279.00 

279.00 

295.42 

293.13 

291.10 

289.60 

288.58 

.85 

1.59 

6.39 

12.40 

10.35 

8.13 

6.05 

10.34 

10.96 

5.55 

2.92 

.52 

1.00 

2.28 
11.32 
20.34 
22.07 
13.26 

2.56 

3.46 
11.63 

7.94 

72.46 

61.14 

40.79 

37.41 

24.15 

21.59 

55.50 

43.87 

73.29 

73.29 

88.52 

121.65 

119.28 

156.65 

173.16 

172.73 

172.44 

171.60 

208.04 

241.16 

239.96 

239.96 

256.42 

254.90 

253.27 

252.41 

252.41 

3.05 
15.63 
33.28 
54.21 
35.44 
10.59 
16.04 
20.95 
18.10 
...„.„„ 

4.78 
1.95 

1.47 

4.16 

11.98 

16.59 

9.35 

2.06 

.43 

2.10 

1.99 

"r.38 
.97 
.27 

73.27 

69.11 

57.13 

59.22 

49.87 

47.81 

84.75 

82.65 

118.02 

118.02 

135.33 

171.72 

171.45 

208.82 

227.28 

227.12 

226  85 

226.53 

263.57 

300.66 

300  66 

300.41 

318.69 

318.44 

317.92 

317.47 

317.47 

1.96 
5.68 

17.34 

18.69 

29.05 
15.80 

Mar.  12 
April  13 
June  10 
July  16 
Aug.  23 
Oct.   21 
April    1 
July  14 
Aug.  9 
Oct.  31 
Jan.   3 

37.37 

4.13 
.90 

37.37 

2.48 
2.41 

18.69 
37.37 
37.37 

3.46 
4.23 
2.38 

1.17 
.72 
.16 

18.69 

2.53 

1.72 

.56 

.59 

.79 

2.33 

3.12 

1.28 
.80 
.27 
.28 
.38 
.94 

1.11 

M 

.77 
.69 
.51 
.35 

2.17 
.43 
.29 
.84 
.93 
4.25 
1.20 

■"2.22 

1.52 

1.63 

.86 

1.39 
.25 
.17 
.48 
.54 

2.05 
.50 

.22 
.16 
.27 
.32 
.34 
.27 

.11 
.07 

Jan.   24 

.12 

Feb.   11 

.14 

Mar.  6 
Aug.  8 
Oct.   10 

37.37 
37.37 

.15 
.10 

Oct.  23 

18.69 

.25 
.41 
.25 
.52 
.45 

.08 

Dec.  21 

2.26 
2.28 
2.03 
1.49 
1.02 

.92 
.59 
.64 
.34 

.14 

Jan.   6 

.08 

Jan.  25 

.16 

April   5 
May  17 

37.37 

.14 

tions.  Allowing  for  this  factor,  however,  the  losses  of  nitrogen 
still  remain  very  large.  During  the  10  month  period  a  loss  of 
nitrogen  equivalent  to  over  800  pounds  nitrate  of  soda  per  acre 
was  noted.  The  losses  of  potash  and  phosphoric  acid  were  much 
smaller,  in  fact,  almost  negligible.  The  loss  of  potash  per  acre 
amounted  to  about  14  pounds,  and  phosphoric  acid  to  about  a 
half  pound.  These  figures  show  that  these  two  elements  of  plant 
food  are  locked  up  in  the  soil  in  relatively  insoluble  forms  which 
become  only  slowly  available.  At  the  end  of  this  period  of  10 
months,  an  orange  tree  was  placed  in  each  tank  and  fertilized 
with  a  fertilizer  of  the  same  formula  as  that  used  in  the  grove 
experiment.  The  trees  in  all  the  tanks  received  the  same  amounts 
of  phosphoric  acid  and  potash  in  the  form  of  acid  phosphate  and 
high  grade  sulphate  of  potash,  the  source  of  nitrogen  only  being 
varied.  The  trees  in  tanks  1  and  2  received  sulphate  of  ammonia, 
the  tree  in  tank  3  nitrate  of  soda,  the  tree  in  tank  4,  dried  blood. 


Bulletin  154,  Citrus  Fertilizer  Experiments  11 

the  same  amount  of  actual  nitrogen  being  used  for  each  tree. 
The  same  amount  of  fertilizer  as  was  used  in  the  grove  was 
applied  to  each  tree  three  times  per  year.  The  results  of  the 
analyses  of  the  drainage  water  collected  from  these  tanks  from 
time  to  time  are  given  in  Table  4.  These  figures  indicate  the 
extent  to  which  the  nitrogen  of  the  three  materials  used  leaches 
thru  the  soil.  These  losses  are  stated  here  in  percentages  of  the 
total  amount  of  nitrogen  applied  less  the  amounts  lost  on  pre- 
ceding dates.  For  example,  the  table  shows  that  on  November 
22,  1911,  the  drainage  water  from  the  nitrate  of  soda  tank 
contained  an  amount  of  nitrogen  equivalent  to  over  54  percent 
of  the  total  nitrogen  which  had  been  applied  up  to  that  date, 
less  the  quantity  of  nitrogen  already  leached  out  up  to  the 
same  date.  In  other  words,  the  percentage  of  loss  for  each 
date  was  figured  on  the  amount  of  nitrogen  still  remaining  in 
the  soil  at  that  date,  and  not  on  the  total  amount  which  had 
been  applied. 

LOSS  OF  NITROGEN 

A  study  of  the  table  brings  out  a  number  of  interesting  and 
important  facts.  It  will  be  noted  that  while  the  loss  of  nitrogen 
varies  with  the  material  used,  the  percentages  lost  with  all  three 
materials  increase  from  the  beginning  up  to  November  22,  and 
continue  large  until  August,  1913.  For  the  period  from  July 
13,  1911  to  July  17,  1913,  41  percent  of  the  sulphate  of  ammonia 
applied  to  the  soil  leached  thru  and  was  lost  in  the  drainage 
water;  72.5  percent  of  the  nitrate  of  soda,  and  38.3  percent  of 
the  dried  blood  were  lost.  This  interval  of  about  two  years 
represents  a  period  during  which  the  trees  were  becoming  estab- 
lished and  when  the  root  system  was  small  and  occupied  but  a 
small  portion  of  the  soil.  Consequently,  much  of  the  fertilizer 
was  not  utilized  and  as  a  result  leached  thru  the  soil  and  was 
lost.  The  fact  that  the  losses  became  smaller  as  time  went  on 
indicates  that  the  larger  root  systems  were  able  to  utilize  more 
and  more  of  the  fertilizer.  The  table  also  brings  out  important 
differences  in  the  behavior  of  the  three  different  sources  of 
nitrogen  in  the  soil.  It  will  be  noted  that  the  largest  loss  of 
nitrogen  occurred  with  the  nitrate  of  soda,  the  losses  from  the 
other  two  sources  being  considerably  less.  The  larger  loss  of 
nitrate  of  soda  is  explained  by  the  fact  that  this  material  is 
very  readily  soluble  in  the  soil  moisture  and  that  the  soil  has 
very  little  if  any  power  to  retain  or  fix  nitrogen  in  the  nitrate 
form.     Consequently,   if  the   soil   is  moist  and  the   rainfall  is 


12  FloHda  Agricultural  Experiment  Station 

sufficient  to  more  than  saturate  the  soil  the  nitrate  of  soda  is 
immediately  dissolved  and  much  of  it  is  carried  below  the  range 
of  the  plant  roots.  Dried  blood  and  sulphate  of  ammonia  differ 
from  nitrate  of  soda  in  their  behavior  in  the  soil. 

The  nitrogen  in  these  materials  is  not  available  for  plants 
until  it  is  changed  to  the  nitrate  form  thru  the  agency  of  various 
soil  bacteria  in  the  process  known  as  nitrification.  In  its  original 
form  the  nitrogen  of  dried  blood  is  not  readily  soluble  in  the 
soil  water,  and  consequently  very  little  is  lost  in  the  leaching 
process  until  nitrification  occurs.  In  this  change  the  organic 
nitrogen  of  the  blood  is  changed  first  to  ammonia,  then  to  the 
nitrite  and  finally  to  the  nitrate  form,  when  it  becomes  as 
readily  soluble  as  the  nitrate  of  soda  and  is  leached  out  as 
readily.  Nitrification  of  the  dried  blood  is  a  gradual  process, 
extending  over  a  period  of  time  which  may  be  of  several  weeks' 
duration,  depending  on  soil  conditions.  Because  of  this,  some 
of  the  nitrogen  of  dried  blood,  or  for  that  matter,  any  similar 
organic  material,  will  remain  in  the  soil  a  considerably  longer 
time  and  be  available  to  the  crop  over  a  longer  period,  than 
nitrate  of  soda.  This  is  especially  true  where  heavy  rains  occur 
after  the  latter  has  been  applied  to  the  soil. 

The  behavior  of  sulphate  of  ammonia  in  the  soil  is  different 
from  either  of  the  two  materials  already  discussed.  While  this 
substance  is  readily  soluble  in  the  soil  water  the  soil  has  the 
power  of  fixing  or  absorbing  at  least  a  portion  of  the  ammonia, 
thus  preventing  it  from  leaching  away.  This  takes  place  thru 
chemical  means  and  is  common  to  all  soils.  Very  sandy  soils  can 
absorb  only  a  small  amount  of  ammonia;  loam  and  clay  soils 
are  able  to  absorb  much  larger  quantities,  due  mainly  to  the  clay 
content  of  these  soils.  Therefore,  when  sulphate  of  ammonia  is 
applied  to  the  soil  at  least  a  part  of  the  ammonia  is  absorbed 
by  this  clay  present  and  fixed  in  a  form  which  is  not  readily 
washed  out.  This  ammonia  must  be  changed,  thru  the  agency  of 
the  nitrifying  bacteria  of  the  soil,  to  the  nitrate  form.  Then 
it  gradually  becomes  available  to  the  plant  and,  of  course,  is 
then  subject  to  leaching.  These  facts  account  for  the  smaller 
loss  of  nitrogen  as  noted  in  the  table,  from  the  soil  receiving 
sulphate  of  ammonia  as  compared  with  that  receiving  nitrate 
of  soda. 

It  should  be  remembered  that  the  three  sources  of  ammonia 
here  discussed  were  used  side  by  side,  in  the  same  equivalent 
amounts,  on  the  same  type  of  soil  and  under  identical  conditions 
so  far  as  these  could  be  brought  about  in  the  experimental  work. 


Bulletin  154,  Citrus  Fertilizer  Experiments 


13 


Accor(iingly,  the  behavior  of  each  of  these  materials  in  the  soil 
as  compared  with  the  others  may  be  taken  as  strictly  compara- 
tive not  only  in  this  experiment  but  under  all  usual  conditions 
where  they  are  used.  The  actual  amount  of  each  which  might  be 
lost  in  the  drainage  on  different  types  of  soil  and  under  varied 
conditions  would  in  all  probability  differ  more  or  less  from  the 
results  given  in  the  table.  However,  the  fact  that  nitrate  of 
soda  for  instance,  leaches  thru  to  a  much  larger  extent  than 
sulphate  of  ammonia,  would  hold  true  under  all  ordinary  con- 
ditions. The  important  facts  brought  to  light  in  the  experimental 
work  here  described  regarding  these  nitrogenous  materials  and 
which  have  a  practical  application  in  grove  fertilization  are  as 
follows :  Nitrogen,  the  most  expensive  ingredient  of  fertilizers 
under  normal  conditions  and  usually  the  element  most  deficient 
in  Florida  soils,  is  the  element  which  is  lost  in  the  largest 
amounts  by  leaching. 

TABLE  5. — Loss  of  Potash  by  Leaching 


I 

Tank   1 

Tank  3 

Tank  4 

5 

1 
O 

«        ! 
tn  _ 

'5 

a:               ^ 

'5 

?  — 

■5 
0^         -S 

1 

in 

S-2 

IS! 

O           O 

0         0 

July 

13 

108.86 

.10  108.76 

.09 

.30  108.56 

.27 

.40  108.46 

.37 

Auk- 
Sept 

23 
5 

.10  108.66 
.70  107.96 

.09 

.64 

.70  107.86 
1.20  106.66i 

.64 
1.11 

.50  107.96 
.80  107.16 

.46 

.74 

Nov. 

22 

72!j37 

1.30  179.23 

1.20 

2.30  176.93 

2.15 

.80  178.93 

.74 

Jan. 

8 
12 

2.40  176.83 
3.50  173.33 

1.34 
1.98 

4.20  172.73 
3.90  168.83 

2.37 
2.26 

1.10  177.83 
2.20  175.63 

.61 

Mar. 

54^43 

1.24 

Apri 

13 

2.90  224.86 

1.67 

4.10  219.16 

2.43 

2.00  228.06 

1.14 

June 

10 

54.43 

9.60  215.26 

4.27 

8.40  210.76 

3.83 

5.40  222.66 

2.37 

July 
Aujr. 

16 
23 

21 

11.80  257.89 
10.80  247.09 
11.10  308.56 

5.48 
4.19 
4.49 

4.30  2(50.89 

2(50.89 

12.20  321.26 

2.04 

3.90  273.19 

273.19 

5.10  340.(56 

1 .75 

Oct. 

72.57 

4^68 

"1.86 

Apri 

1 

54.43 

7.10  355.89 

2.30 

6.80  368.89 

2.11 

6.60  388.49 

1.94 

July 

14 

54.43 

6.50  349.39 

1.83 

6.60  362.29 

1.79 

6.90  381.59 

1.77 

AuK- 

9 
31 

72.57 

40.3. 82 
10.10  466.29 

2.50 

416.72 

17.00  472.29 

436.02 

3.20  505.39 

Oct. 

4.08 

.73 

Jan. 

3 
24 

1(5.00  450.29 
7.50  442.79 

3.43 
1 .6(5 

22.50  449.79 
14.70  435.09 

4.7(5 
3.27 

(5.70  498.(59 
10.90  487.79 

1.32 

Jan. 

2.18 

Feb. 

11 

7.00  435.79 

1.58 

11.20  423.89 

2.57 

13.60  474.19 

2.79 

Mar. 

(5 

54.43 

8..30  481.92 

1.90 

10.20  468.12 

2.41 

10.20  518.42 

2.15 

Aujr. 

8 

54.43 

13.40  522.95 

2.78 

11.20511.35 

2.39 

5.50  5(57.35 

1.0*5 

Oct. 

10 
23 
21 

19.80  503.15 
503.15 

3.79 

6.20  505.15 

505.15 

13.40  564.32 

1.21 

2^(55 

5(57. .35 

3.90  5(53.45 
10.30(525.72 

Oct. 

72.57 

.(59 

Dec. 

14.60  561.12 

2.90 

1.83 

Jan. 

(5 

12.40  548.72 

2.21 

11.40  552.92 

2.02 

8.40  61  7. ••'.2 

1.34 

Jan. 

2.") 

13.40  535.32 

2.44 

11.80  541.12 

2.13 

8.10  (509.22 

1.31 

Apri 

rt 

54  4:'. 

1(5  50  518.82 

3.0S 

13.;>0  527.22 

2  57 

12.(^0  597.22 

1.97 

.Mav 

17 

9.60  573.25 

1 .85 

5s;i.(;5 

(551.(55 

14  Florida  Agricultural  Experiment  Station 

The  various  sources  of  nitrogen  differ  greatly  in  their  tendency 
to  leach  out  of  the  soil,  much  more  of  the  nitrogen  of  nitrate  of 
soda  than  of  sulphate  of  ammonia  being  lost  in  this  way. 

The  greatest  losses  take  place  when  heavy  rains  occur  soon 
after  an  application  of  nitrogenous  fertilizers. 

These  losses  decrease  to  a  great  extent  as  the  trees  become 
older  and  more  of  the  soil  becomes  permeated  with  tree  roots. 

LOSS  OF  POTASH 

Table  5  shows  that  a  considerable  loss  of  potash  has  taken 
place.  The  figures  in  the  potash  column  represent  the  average 
losses  for  three  soil  tanks.  The  losses  for  the  first  two  years 
are  small,  after  which  they  increase  considerably.  This  would 
indicate  that  during  the  first  period  part  of  the  potash  applied 
was  absorbed  by  the  soil,  but  that  after  the  second  year  the 
soil  had  reached  its  maximum  capacity  for  holding  the  potash 
and  became  saturated,  so  to  speak,  so  that  succeeding  applica- 
tions were  not  absorbed  to  any  extent. 

It  is  well  known  that  practically  all  soils  have  some  power  to 
retain  soluble  potash.  Sandy  soils  exhibit  this  capacity  in  the 
least  degree,  while  heavy  clay  soils  will  absorb  large  amounts. 
The  power  of  a  soil  to  fix  or  absorb  potash  depends  largely  upon 
the  presence  of  certain  silicates  which  are  associated  with  the 
clay  present.  When  absorbed  by  the  soil,  water-soluble  potash 
assumes  a  form  which  is  not  easily  leached  out  by  water  but 
which  is  still  generally  regarded  as  being  more  available  to 
plants  than  the  potash  combinations  originally  present.  Since 
Florida  soils  as  a  general  rule  contain  very  little  clay  their  power 
to  absorb  potash  is  limited.  In  the  work  here  described  it  was 
found  that  at  the  end  of  four  years  about  30  percent  of  the 
potash  applied  had  leached  out,  the  remaining  70  percent  being 
used  by  the  trees  or  absorbed  by  the  soil.  In  bearing  groves  the 
loss  by  leaching  would  undoubtedly  be  under  rather  than  over 
the  30  percent  found  here. 

LOSS  OF  PHOSPHORIC  ACID 

No  table  is  included  to  show  the  loss  of  phosphoric  acid  since 
this  loss  has  been  extremely  small.  At  the  end  of  four  years  it 
was  found  that  only  .05  of  one  percent  of  the  amount  applied  was 
lost  in  the  drainage  water.  This  indicates  that  the  soil  is  able 
to  absorb  large  amounts  of  soluble  phosphoric  acid.  That  this 
is  true  is  shown  by  the  fact  that  the  soil  used  contained  50  per- 
cent more  phosphoric  acid  at  the  end  of  five  years  than  it  did  at 
the  beginning  of  the  experiment. 


Bulletin  154,  Citrus  Fertilizer  Experiments 


15 


TABLE  6. — Increase  in  Phosphoric  Acid  Content  of  Soil 


Source  of 
Phosphoric  Acid 


cu 


1. 

2. 
3 

4. 

5. 

6. 

7. 

8. 

9. 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 


Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Ac 
Dis 


phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
phosphate 
bone  black. 


Steamed   bone   . 

26 jSteamed   bone   . 

27 JBasic  slag  

28 |Basic  slag  

29 lAcid  phosphate 

30 jAcid  phosphate 

31 lAcid   phosphate 

32 jDis.  bone  black. 

33 Floats  

34 Floats  

35 Floats  

36 Floats  

37 Acid  phosphate 

38 Acid   phosphate 

39 Acid  phosphate 

40 Acid   phosphate 

41 lAcid  phosphate 

42 1  Acid   phosphate 

43 !No  fertilizer  

44 1  Acid   phosphate 

45 Acid   phosphate 

46 JAcid   phosphate 

47 lAcid  phosphate 

48 Acid   phosphate 


o- 

(M. 

CLhOh 

2859 

3601 

4532 

4750 

3701 

4080 

3513 

3082 

3720 

3213 

3783 

3357 

3916 

3659 

3396 

4372 

4286 

3861 

3598 

3472 

3456 

3516 

4210 

4115 

3609 

4524 

3643 

3901 

3559 

3434 

4145 

3530 

3197 

4095 

4091 

4466 

3270 

3877 

3507 

3529 

3432 

3510 

3348 

3815 

3735 

3716 

3192 

3529 


P205  in 
Check 

Increase 
in  Total 

Increase 
in  Acid- 
Soluble 

2633 

226 

200 

3002 

599 

480 

3449 

1083 

850 

3037 

1713 

1660 

3037 

664 

750 

3449 

631 

720 

3002 

511 

450 

2633 

449 

300 

3238 

482 

320 

2895 

318 

310 

3356 

427 

390 

3177 

180 

380 

3177 

739 

630 

3356 

303 

440 

2895 

501 

530 

3469 

903 

600 

3794 

492 

290 

3554 

307 

280 

2959 

639 

450 

2839 

633 

310 

2839 

617 

410 

2959 

557 

630 

3554 

656 

370 

3794 

321 

430 

3098 

511 

230 

3651 

873 

510 

3033 

610 

340 

3236 

665 

630 

3236 

323 

340 

3037 

397 

400 

3651 

494 

440 

3098 

432 

450 

2904 

293 

330 

3191 

904 

650 

3035 

1056 

1010 

2795 

1671 

1400 

2795 

475 

420 

3035 

842 

540 

3191 

316 

420 

2904 

625 

510 

2997 

435 

300 

2820 

690 

520 

3348 

0 

—30 

3142 

673 

380 

3142 

593 

490 

3348 

368 

320 

2860 

332 

400 

2997 

532 

460 

PHOSPHORIC  ACID 

In  studying  the  effect  of  the  fertilizers  used  on  the  composition 
of  the  soil,  especial  attention  was  given  to  the  phosphoric  acid. 
Work  at  the  Experiment  Station  with  soil  tanks  has  shown  that 
the  loss  of  phosphoric  acid  in  the  drainage  water  where  acid 


16  Florida  Agricultural  Experiment  Station 

phosphate  was  used  was  so  small  as  to  be  negligible,  and  that 
practically  all  the  phosphoric  acid  applied  was  retained  by  the 
soil.  The  work  with  the  grove  soils  has  confirmed  these  results. 
Samples  of  soil  from  the  fertilized  plots  and  from  the  middle  of 
the  tree  rows  were  taken  from  time  to  time  to  a  depth  of  9  inches, 
and  determinations  made  of  the  phosphoric  acid.  Work  else- 
where has  shown  that  the  greater  part  of  the  phosphoric  acid 
absorbed  by  soils  is  retained  in  the  upper  plowed  soil,  so  in  this 
work  sampling  to  a  depth  of  9  inches  was  considered  sufficient. 
The  difference  between  the  amount  of  phosphoric  acid  in  the 
soil  of  the  plot  and  that  in  the  corresponding  middle  would  show 
the  quantity  fixed  by  the  soil.  These  results  for  the  different 
plots  are  given  in  Table  6.  In  order  to  make  the  results  easily 
comparable  they  have  been  calculated  to  pounds  per  acre.  The 
figures  in  the  table  represent  in  every  instance  the  average  of 
the  results  obtained  from  three  different  samplings  of  soil,  the 
third  being  taken  in  July,  1915.  The  second  column  from  the 
right  shows  the  increase  in  phosphoric  acid  content,  due  to  the 
absorption  by  the  soil  of  the  phosphate  fertilizer  applied.  It 
will  be  noted  that  these  figures  vary  considerably  among  them- 
selves, even  where  the  amount  and  form  of  phosphoric  acid 
applied  has  been  identical.  This  variation  can  be  accounted  for 
by  the  difficulty  of  obtaining  samples  of  soil  which  are  perfectly 
representative  of  the  plots.  However,  it  will  be  noted  that  those 
plots  receiving  the  largest  applications  of  fertilizer  also  show 
the  greatest  amounts  of  phosphoric  acid  retained.  Plot  4,  re- 
ceiving four  times  the  standard  quantity  of  fertilizer  shows 
the  greatest  fixation,  an  increase  of  1713  pounds  per  acre  being 
noted.  The  source  of  the  phosphoric  acid  on  this  plot  was  acid 
phosphate.  Plot  36  receiving  the  same  amount  of  actual  phos- 
phoric acid  as  plot  4,  but  in  the  form  of  floats,  shows  a  gain 
practically  the  same  as  plot  4.  Both  these  plots  show  an  increase 
of  over  50  percent.  Altho  five  different  sources  of  phosphoric 
acid  were  used  on  the  plots,  the  form  in  which  it  was  used  does 
not  appear  to  have  had  any  influence  on  the  power  of  the  soil 
to  absorb  this  material,  the  water-soluble  form  being  retained 
as  thoroly  as  the  insoluble  forms. 

CHANGES  OF  PHOSPHORIC  ACID   IN   SOIL 

It  is  believed  that  the  figures  in  the  last  column  of  Table  6 
throw  some  light  on  the  question  as  to  what  forms  the  phos- 
phoric acid  assume  after  being  incorporated  with  the  soil.  It  is 
generally  agreed  upon  among  soil  investigators  that  the  phos- 


Bulletin  154,,  Citrus  Fertilizer  Experiments  .17 

phoric  acid  of  the  soil  exists  mainly  in  three  forms,  namely,  the 
phosphates  of  lime,  iron,  and  alumina.  It  is  generally  considered 
that  the  last  two  forms  are  much  less  available  to  plants  than 
the  first  form.  Indeed  it  is  held  by  many  that  the  phosphates 
of  iron  and  alumina  are  but  very  slightly  available  because  of 
their  practical  insolubility  in  the  soil  water.  Phosphate  of  lime, 
on  the  other  hand,  dissolves  slowly  in  the  soil  water  containing 
carbonic  acid  gas  and  other  weak  acids  and  is  thus  considered 
more  available  to  plants.  The  fixation  of  soluble  phosphoric  acid 
in  the  soil  is  explained  by  the  fact  that  it  combines  with  one  or 
more  of  the  compounds  of  iron,  aluminum  or  lime  present  and 
thus  assumes  an  insoluble  form.  It  then  becomes  a  matter  of 
some  practical  importance  to  know  whether  the  phosphoric  acid 
added  to  the  soil  assumes  the  form  of  the  insoluble  iron  and 
aluminum  phosphates  or  the  more  readily  available  phosphate  of 
lime.  A  method  of  treatment  which  it  is  believed  will  distinguish 
between  the  different  forms  has  been  developed  by  soil  chemists 
and  has  been  used  to  some  extent.  It  depends  upon  digesting  the 
soil  in  a  weak  solution  of  nitric  acid,  which  will  dissolve  the 
phosphate  of  lime  present  but  which  has  no  effect  upon  the 
phosphate  of  iron  and  alumina.  A  given  weight  of  soil  was 
treated  with  fifth-normal  nitric  acid  (about  1.26  percent  acid) 
and  the  amount  of  phosphoric  acid  dissolved  out  determined,  this 
dissolved  phosphoric  acid  being  regarded  as  coming  entirely 
from  the  phosphate  of  lime  present.  The  soil  samples  used  were 
those  on  which  the  total  phosphoric  acid  had  been  determined  as 
shown  in  the  table.  The  results  given  in  the  table  represent  the 
difference  between  the  amounts  dissolved  from  the  plot  soils 
and  those  of  the  corresponding  middles,  thus  representing  the 
increase  in  the  acid  soluble  phosphoric  acid  of  the  fertilized 
plots,  and  are  calculated  to  pounds  per  acre. 

Some  interesting  facts  are  brought  out  by  comparing  these 
results  with  the  figures  representing  the  increase  in  total  phos- 
phoric acid.  Those  plots  showing  the  greatest  increase  in  total 
phosphoric  acid  also  show  the  greatest  increase  in  acid-soluble. 
Plot  4  again  shows  the  greatest  increase,  followed  by  plot  36. 
The  average  increase  in  acitl-soluble  phosphoric  acid  for  all  the 
plots  (omitting  plot  43)  is  494  pounds,  as  compared  with  an 
average  increase  in  total  of  586  pounds.  Assuming  that  the 
acid  used  dissolved  out  only  phosphate  of  lime  and  no  iron  or 
aluminum  phosphate,  these  figures  indicate  that  about  80  percent 
of  the  increase  in  phosphoric  acid  content  in  the  plots  has  been 
fixed  in  the  form  of  phosphate  of  lime. 


18 


Florida  Agj-icultural  Experiment  Station 


TABLE  7. 

—Nitrogen  Content  of  Plot  Soils 

Plot 

;  Nitrogen 

Nitrogen 

Plot 

Nitrogen 

Nitrogen 

in  Plot 

in  Middle 

in  Plot 

in  Middle 

1 

1140 

780 

25 

1350 

1020 

2 

1170 

990 

26 

1080 

930 

3 

1080 

1050 

27 

1110 

1080 

4 

810 

1140 

28 

1140 

1140 

5 

870 

1140 

29 

1290 

1140 

6 

1170 

1050 

30 

1020 

1080 

7 

1140 

990 

31 

1230 

930 

8 

1140 

780 

32 

1440 

1020 

9 

1080 

840 

33 

1200 

1050 

10 

990 

1110 

34 

1140 

1050 

11 

1170 

990 

35 

1170 

1140 

12 

1140 

1020 

36 

1230 

1050 

13 

1410 

1020    1 

37 

1320 

1050 

14 

1440 

990 

38 

1410 

1140 

15 

1410 

1110 

39 

1080 

1050 

16 

1230 

840 

40 

1110 

1050 

17 

1170 

960 

41 

1230 

810 

18 

1260 

1080 

42 

1380 

1140 

19 

1260 

1080 

43 

900 

990 

20 

1230 

990 

44 

1230 

1290 

21 

1320 

990 

45 

1920 

1290 

22 

1350 

1080 

46 

720 

990 

23 

1260 

1080 

47 

780 

1140 

24 

1440 

960 

48 

720 

810 

NITROGEN 

Table  7  gives  the  amount  of  nitrogen  in  pounds  per  acre  to  a 
depth  of  9  inches.  The  soil  samples  were  taken  from  the  plots 
and  from  the  middles  at  the  end  of  the  experiment  in  1918.  One 
fact  brought  out  here  is  the  considerably  smaller  amount  of 
nitrogen  in  the  clean  culture  plots,  46,  47  and  48,  as  compared 
with  the  remaining  forty-five  plots.  The  average  amount  of 
nitrogen  in  these  three  plots  is  740  pounds  per  acre,  as  compared 
with  an  average  for  the  others  of  1220  pounds  an  acre,  indicating 
a  loss  of  480  pounds  or  39  percent.  This  loss  must  be  attributed 
largely  to  the  effects  of  the  continuous  cultivation.  This  practice 
leads  to  more  rapid  nitrification  of  the  organic  nitrogen  of  the 
soil,  changing  the  insoluble  nitrogen  to  the  soluble  nitrate  form 
which  is  easily  leached  out.  This  loss  of  organic  matter  also 
means  a  decrease  in  the  capacity  of  the  soil  for  holding  moisture 
and  soluble  fertilizers  added  to  it. 

The  average  of  the  forty-eight  soils  taken  from  the  middles 
is  1030  pounds  of  nitrogen  per  acre.  It  is  interesting  to  compare 
this  figure  with  the  average  of  fifteen  samplings  taken  at  the 
beginning  of  the  experiment  in  1909.  These  samples  were  taken 
at  various  places  over  the  field  and  probably  give  a  fair  average 
of  the  nitrogen  content  at  that  time.     The  amount  of  nitrogen 


Bulletin  15 Jf.,  Citrus  Fertilizer  Expe7'iments 


19 


found  in  this  way  was  1080  pounds  per  acre.  This  is  so  close 
to  the  average  for  the  middles  (1030  pounds)  at  the  end  of  the 
experiment  that  it  is  reasonable  to  assume  that  the  unfertilized 
soil  between  the  tree  rows  neither  gained  nor  lost  in  nitrogen 
during  the  ten  years.  In  other  words,  the  loss  of  nitrogen  thru 
leaching  was  counterbalanced  by  the  addition  of  nitrogen  by 
means  of  the  leguminous  cover  crop.  The  fertilized  plots  have 
gained  slightly  in  nitrogen  as  compared  with  the  soils  from  the 
middle  of  the  rows.  Omitting  the  clean  culture  plots  and  the  no 
fertilizer  plot,  the  average  is  1220  pounds  per  acre,  a  gain  over 
the  middles  of  190  pounds. 

TABLE  8. — Potash  Content  of  Plot  Soils  at  End  of  Experiment-in  1918 


Plot 


Potash 


Plot 


Potash 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 


22 

23  

24^_. 

Unfertilized  soil  1140 


1620 

25 

1800 

26 

2010 

27 

2040 

28 

1740    i 

29 

1830 

30 

1740 

31 

1740    I 

32 

1830 

33 

1530 

34 

1740 

35 

1950 

36 

1830 

37 

1950 

38 

1620 

39 

1740 

40 

1530 

41 

1740 

42 

2160 

43 

1950 

44 

2250 

45 

1950 

46 

1440 

47 

2040 

48 

2160 
1530 
2070 
1950 
1620 
2040 
1950 
2040 
1440 
1950 
1530 
1830 
1830 
2160 
1440 
1680 
1950 
1830 
1140 
1830 
1620 
1620 
1440 
1530 


POTASH  IN  GROVE  SOIL 

The  amount  of  potash  present  in  the  different  plots  at  the 
end  of  the  experiment  in  1918  is  given  in  Table  8.  The  results 
are  calculated  in  pounds  per  acre  to  a  depth  of  9  inches,  and 
represent  the  total  amount  of  potash  in  the  soil  to  that  depth. 
The  unfertilized  middles  were  also  sampled,  and  potash  deter- 
mined in  seven  of  these  soils.  The  average  of  these  seven  soils 
amounts  to  1140  pounds  per  acre.  By  comparing  this  figure  with 
those  for  the  various  plots,  the  increase  in  the  latter  due  to  the 
potash  in  the  fertilizer  may  be  determined.    It  will  be  noted  that 


20 


Florida  Agricultural  Experiment  Station 


TABLE  9. — Gain  in  Diameter  of  Trees  for  10  Years 


Gain 


Fertilizer  Treatment 


139 
138 
136 
134 
133 
132 
130 
130 
128 
127 
127 
127 
126 
125 
124 
124 
123 
123 
122 
121 
120 
118 
114 
114 
114 
113 
112 
112 
111 
111 

110 
110 
110 
109 
109 
108 
107 
106 
105 
104 
103 
102 
101 
96 

90 

88 
75 
65 


Standard. 

One-half  standard. 

Standard  and  air-slaked  lime. 

Standard.     Mulched. 

Nitrogen  from  dried  blood.     Clean  culture. 

Standard.     Clean  culture. 

Nitrogen,  %  nitrate  of  soda,  %  sulphate  of  ammonia. 

Standard.     Mulched. 

Standard. 

Nitrogen  from  nitrate  of  soda.     Clean  culture. 

Potash  from  low-grade  sulphate. 

Phosphoric  acid  from  steamed  bone. 

Nitrogen,  ^  cottonseed  meal,  V^  sulphate  of  ammonia. 

Phosphoric  acid  and  potash  decreased   by  one-half. 

Acid  phosphate,  nitrate  of  soda,  hardwood  ashes. 

Standard. 

Phosphoric  acid  and  potash  increased  by  one-half. 

Phosphoric  acid  from  floats.    (4  times  amt.)    Cottonseed  meal. 

Phosphoric  acid  from  floats.     (4  times   amt.) 

Phosphoric  acid  and  nitrogen  decreased  by  one-half. 

Potash  from  muriate. 

Standard. 

Nitrogen  from  cottonseed  meal.    Ground  limestone. 

Nitrogen,   ^  cottonseed  meal,  %   nitrate  of  soda. 

Twice  standard. 

Nitrogen  from  cottonseed  meal. 

Phosphoric  acid  from  steamed  bone.   (2  times  amt.) 

Phosphoric  acid  from  dissolved  bone  black. 

Phosphoric  acid  from  floats.   (2  times  amt.) 

Potash  from  nitrate  of  potash.     Balance  nitrogen,  nitrate  of 

soda. 
Nitrogen,  %  nitrate  of  soda,  V2  dried  blood. 
Standard  and  ground  limestone. 
Phosphoric  acid  from  dissolved  bone  black. 
Nitrogen  from  nitrate  of  soda. 

Phosphoric  acid  from  Thomas  slag.    Nitrate  of  soda. 
Nitrogen  and  potash  increased  by  one-half. 
Phosphoric   acid  from   floats. 

Nitrogen,  V2  sulphate  of  ammonia,  V2  dried  blood. 
TV2  percent  potash  in  June,  TV2  in  October,  3  in  February. 
Potash   from   kainit. 
Standard. 

Nitrogen  and  potash  decreased  by  one-half. 
No  fertilizer. 
Phosphoric  acid  from  Thomas  slag.  (2  times  amt.)  Nitrate  of 

soda. 
Nitrogen  from  dried  blood. 
Standard.     Ground   limestone. 

Phosphoric  acid  and  nitrogen  increased  by  one-half. 
Four  times  standard. 


all  the  fertilized  plots  show  an  increase  over  the  unfertilized 
soil,  thus  indicating  that  this  soil  was  able  to  retain  at  least 
a  portion  of  the  soluble  potash  applied.  The  average  increase 
for  the  forty-seven  plots  amounts  to  660  pounds  per  acre,  or  an 
increase  of  over  50  percent  for  the  ten  years  of  the  experiment. 
A  large  proportion  of  the  potash  in  the  plot  soils  is  held  in 


Bulletin  154,  Citrus  Fertilizer  Experiments 


21 


a  very  insoluble  form,  probably  largely  as  feldspar.    Treatment 
of  these  soils  with  strong  hydrochloric  acid  dissolved  on  the 
average  only  15  percent  of  the  total  potash  present. 
TABLE  10.— Rank  of  Plots 


Rank 

1910 

1911 

1912 

1913 

1914 

1915 

1916 

1917 

1918 

1 

46 

46 

46 

47 

2 

2 

2 

2 

2 

2 

30 

47 

47 

46 

1 

47 

1 

1 

1 

3 

45 

35 

35 

36 

47 

1 

46 

47 

12 

4 

41 

41 

41 

37 

46 

13 

13 

48 

13 

5 

29 

44 

48 

13 

13 

12 

12 

12 

47 

6 

24 

36 

2 

41 

36 

48 

47 

13 

46 

7 

26 

48 

36 

48 

41 

36 

48 

25 

16 

8 

5 

37 

37 

12 

12 

37 

45 

46 

45 

9 

13 

43 

22 

22 

37 

46 

25 

8 

31 

10 

35 

16 

44 

2 

45 

22 

37 

31 

48 

11 

31 

22 

30 

35 

48 

30 

22 

37 

37 

12 

22 

2 

43 

30 

22 

41 

36 

9 

25 

13 

23 

8 

42 

31 

30 

25 

30 

36 

22 

14 

43 

42 

12 

45 

44 

35 

31 

11 

8 

15 

47 

6 

13 

38 

21 

31 

41 

35 

30 

16 

19 

30 

1 

44 

38 

21 

8 

6 

41 

17 

36 

45 

38 

34 

43 

44 

35 

22 

6 

18 

42 

26 

20 

8 

35 

38 

11 

30 

36 

19 

17 

25 

31 

26 

8 

45 

9 

44 

35 

20 

30 

38 

8 

43 

9 

11 

6 

45 

9 

21 

21 

12 

16 

21 

29 

6 

16 

16 

38 

22 

49 

11 

34 

29 

31 

43 

21 

20 

44 

23 

37 

19 

26 

25 

23 

9 

26 

24 

21 

24 

14 

34 

6 

23 

16 

29 

29 

23 

23 

25  - 

15 

31 

29 

42 

32 

23 

38 

32 

3 

26 

8 

33 

33 

20 

42 

8 

32 

29 

20 

27 

27 

39 

23 

32 

25 

16 

23 

26 

26 

28 

44 

20 

11 

6 

24 

32 

44 

21 

32 

29 

32 

24 

32 

28 

20 

34 

20 

38 

34 

30 

34 

29 

19 

1 

11 

26 

24 

42 

42 

31 

6 

1 

45 

33 

6 

24 

3 

3 

19 

32 

38 

7 

25 

9 

39 

15 

34 

19 

11 

33 

35 

13 

7 

11 

34 

20 

19 

15 

24 

34 

4 

27 

21 

39 

33 

42 

43 

10 

15 

35 

3 

9 

39 

24 

26 

28 

28 

14 

27 

36 

25 

32 

9 

19 

15 

10 

42 

34 

7 

37 

16 

14 

24 

7 

7 

3 

15 

27 

33 

38 

10 

23 

14 

3 

3 

33 

27 

33 

18 

39 

18 

21 

27 

10 

19 

39 

33 

43 

29 

40 

40 

3 

3 

15 

10 

19 

7 

18 

40 

41 

11 

5 

28 

18 

14 

27 

10 

7 

14 

42 

21 

28 

10 

14 

40 

7 

14 

40 

10 

43 

9 

17 

40 

27 

17 

14 

18 

41 

43 

44 

12 

10 

15 

40 

27 

40 

40 

28 

28 

45 

28 

40 

17 

16 

18 

18 

39 

17 

17 

46 

2 

15 

5 

5 

28 

5 

17 

39 

39 

47 

1 

18 

18 

17 

5 

17 

5 

5 

5 

48 

7 

4 

4 

4 

4 

4 

4 

4 

4 

EFFECT  OF  FERTILIZERS  ON  GROWTH 

The  effect  of  the  various  fertilizer  treatments  used  in  pro- 
ducing growth  was  measured  each  year  by  taking  the  diameter 
of  the  tree  trunks.    Table  9  gives  the  average  measurements  of 


22  Florida  Agricultural  Experiment  Station 

the  trees  in  the  various  plots  at  the  end  of  the  experiment.  The 
measurements  are  given  in  thirty-seconds  of  an  inch.  These 
figures  were  obtained  by  subtracting  the  original  diameter  of 
the  tree  when  set  out  from  the  final  measurement  at  the  end  of 
1918.  In  each  case  they  are  the  average  of  the  ten  trees  in  each 
plot,  and  give  the  actual  increase  made  by  the  trees.  Similar 
measurements  were  taken  every  year  during  the  continuation  of 
the  experiment.  The  standing  of  the  different  plots  from  year 
to  year,  beginning  with  1910  is  shown  in  Table  10. 

In  Table  9  the  plots  are  arranged  in  the  order  of  the  increase 
in  growth  made  at  the  end  of  the  ten  years,  the  plot  making  the 
largest  increase  being  placed  at  the  head  of  the  list.  This  table 
brings  out  the  fact  that  in  this  experiment  a  number  of  sources 
of  materials  have  proven  almost  equally  valuable  in  producing 
growth  and  that  several  have  had  an  injurious  effect.  Among 
the  fertilizers  used  on  the  plots  making  the  most  growth  no 
single  source  has  shown  any  remarkable  superiority  over  others 
used,  altho  there  is  a  considerable  variation  in  the  effect  of  the 
different  materials.  The  results  of  this  work  emphasize  the  fact 
that  the  citrus  grower  need  not  be  restricted  in  his  choice  of 
fertilizers  to  one  particular  material,  but  that  there  are  a  number 
of  sources  of  the  three  essential  elements  which  can  be  used  to 
advantage.  It  should  be  stated  that  the  soil  on  which  this  ex- 
periment was  located  was  somewhat  above  the  average  in  fer- 
tility, especially  in  phosphoric  acid  content.  This  fact  has  served 
to  minimize  differences  which  might  otherwise  have  developed 
between  the  fertilizers  used  and  especially  the  sources  of  phos- 
phoric acid.  The  behavior  of  plot  43,  w^hich  received  no  fertilizer 
during  the  time  the  experiment  continued  brings  out  the  fact 
that  the  soil  was  unusually  well  supplied  with  plant  food.  How- 
ever, a  study  of  the  table  brings  out  the  fact  that  the  plots  making 
the  best  growth  have  received  the  standard  mixture  of  sulphate 
of  ammonia,  acid  phosphate  and  high  grade  sulphate  of  potash. 
Of  the  best  16  plots,  all  but  one  have  received  acid  phosphate  as 
the  source  of  phosphoric  acid.  The  one  exception  is  plot  number 
25,  receiving  steamed  bone  and  ranking  twelfth  in  the  list.  All 
but  two  plots  in  these  sixteen  have  received  high  grade  sulphate 
of  potash  as  the  source  of  potash.  The  two  exceptions  are  plot 
number  37  receiving  low  grade  sulphate  of  potash  and  plot 
number  30  receiving  hard  wood  ashes,  and  ranking  eleventh  and 
fifteenth,  respectively.  Of  the  five  different  sources  of  nitrogen 
used,  all  are  represented  in  the  best  10  plots.     Sulphate  of  am- 


Bulletin  154,  Citrus  Fertilize!-  Experiments  23 

monia,  nitrate  of  soda,  and  the  nitrogen  of  steamed  bone  have  all 
produced  good  growth.  It  will  be  noted  that  plot  number  2, 
receiving  the  standard  mixture,  stands  at  the  head  of  the  list. 
As  stated  elsewhere,  this  standard  mixture  consisted  of  sulphate 
of  ammonia,  acid  phosphate,  and  high  grade  sulphate  of  potash. 
This  mixture  was  applied  at  the  rate  of  2  pounds  per  tree  three 
times  per  year.  The  amount  was  increased  as  the  trees  increased 
in  size,  the  application  finally  being  at  the  rate  of  6  pounds  three 
times  per  year. 

Plot  number  1,  receiving  one-half  the  standard  amount,  or 
at  the  beginning  1  pound  per  tree  three  times  per  year,  shows 
practically  the  same  increase  in  growth  as  plot  2.  Plot  number 
3,  receiving  twice  the  standard  amount,  or  4  pounds  per  tree  at 
the  beginning  ranks  twenty-fifth,  while  plot  number  4,  receiving 
four  times  the  standard  amount  or  8  pounds  per  tree,  ranks  at 
the  foot,  having  made  less  growth  than  any  of  the  plots.  The 
standing  of  this  series  of  four  plots  brings  out  the  fact  that  in 
this  experiment  plot  number  1  was  receiving  about  the  optimum 
amount  of  fertilizer  which  it  would  pay  to  apply  to  trees  of 
this  age,  and  that  plot  number  2  received  the  maximum  amount 
which  could  be  applied  without  inducing  injury.  The  fact  that 
plots  2  and  1  made  practically  the  same  amount  of  growth  indi- 
cates that  the  former  was  receiving  more  fertilizer  than  the 
trees  could  profitably  use,  altho  not  enough  to  injure  them  in 
any  way.  The  appearance  of  these  two  plots  was  very  similar, 
the  eye  not  being  able  to  detect  any  difference  in  size,  character 
of  growth,  or  appearance  of  the  leaves.  Plot  number  3,  receiving 
twice  the  standard  amount  of  fertilizer  has  developed  consider- 
able injury.  This  injury  was  shown  soon  after  the  beginning  of 
the  experiment,  was  quite  severe  for  several  years,  but  finally 
became  much  less  apparent.  This  would  indicate  that  4  pounds 
per  tree  three  times  per  year  was  about  the  maximum  amount  cf 
fertilizer  which  could  be  applied  to  young  trees  and  not  kill  them 
outright.  The  injury  was  severe  during  the  first  few  years  but 
the  trees  managed  to  survive  and  finally  to  overcome  the  inju- 
rious eff"ects.  The  behavior  of  this  plot  in  thus  overcoming  the 
injurious  effects  of  too  much  fertilizer  is  shown  in  Table  10.  It 
will  be  noted  that  in  1911  and  1912  this  plot  ranked  number  forty 
in  the  list.  In  1913  and  1914  it  rose  to  thirty-eighth;  in  1915  to 
thirty-seventh;  in  1916  and  1917  to  thirty-first;  and  in  1918 
to  twenty-fifth.  This  rise  in  rank  indicates  that  as  the  trees 
became  older  they  were  better  able  to  withstand  the  effects  pro- 


24  Florida  Agricultural  Experiment  Station 

duced  by  too  much  fertilizer.  The  early  injury,  however,  re- 
sulted in  a  permanent  stunting  of  the  trees.  At  the  end  of  the 
experiment  they  were  about  three-fourths  as  large  as  the  trees 
of  plots  1  and  2. 

Plot  4  shows  the  maximum  injury  from  the  use  of  too  much 
fertilizer.  These  trees  were  stunted  from  the  beginning  and  have 
made  very  little  growth.  By  the  winter  of  1912  half  of  the 
trees  in  this  plot  were  dead  and  had  to  be  replaced  by  others. 
In  the  spring  of  1913  the  excessive  applications  were  discon- 
tinued and  from  that  time  on  only  one  pound  per  tree  was  used 
three  times  per  year.  The  new  trees  used  to  replace  those  killed 
by  the  fertilizer  have  failed  to  make  much  growth.  At  the  end 
of  the  experiment  this  plot  was  less  than  one-fourth  the  size 
of  plots  1  and  2  and  consisted  of  almost  worthless  trees  which 
will  probably  never  amount  to  much.  Photographs  of  plots  2, 
3  and  4  are  reproduced  in  Fig.  4. 

The  behavior  of  plots  number  5,  6  and  7  is  interesting  in  this 
connection,  because  of  its  bearing  on  the  question  as  to  which 
of  the  fertilizing  elements  used  was  chiefly  responsible  for  the 
injury  produced.  In  this  series  of  three  plots  two  of  the  elements 
were  increased  by  one-half,  the  third  being  used  in  the  standard 
amount.  In  the  mixture  applied  to  plot  6  the  acid  phosphate  and 
high  grade  sulphate  of  potash  used  was  one  and  one-half  times 
the  amount  used  in  the  standard  mixture,  the  sulphate  of  am- 
monia remaining  the  same  as  in  the  latter.  Plot  7  received  li/^ 
times  the  nitrogen  and  potash  of  the  standard  and  plot  5 
received  li/^  times  the  nitrogen  and  phosphoric  acid  of  the 
standard.  It  will  be  noted  that  the  least  amount  of  growth  was 
made  by  plot  5  which  ranks  forty-seventh  in  the  list.  This  plot 
showed  all  the  signs  of  severe  injury  caused  by  too  much  ferti- 
lizer. In  the  table  showing  the  rank  of  the  plots  by  years  plot 
5  stood  forty-first  in  1911  and  dropped  still  lower  from  year  to 
year,  until  for  the  last  three  years  it  stood  next  to  the  lowest. 

Plot  7,  where  the  nitrogen  and  potash  were  increased,  has 
made  a  better  growth  than  plot  5  but  not  as  much  as  plot  6. 
The  latter  plot  shows  no  injury  from  the  increased  phosphoric 
acid  and  potash  used.  The  trees  in  plot  7  show  some  injury 
caused  by  too  much  fertilizer  but  the  injury  is  not  quite  so 
marked  as  in  plot  5.  The  behavior  of  these  three  plots  brings 
out  the  fact  that  excessive  quantities  of  nitrogen  are  much  more 
injurious  than  similar  quantities  of  phosphoric  acid  and  potatsh 
and  that  increased  ratios  of  nitrogen  and  potash  are  less  inju- 


-WMf' 


^^••^- 


J/ 


ji£i^?ik.;.ift: 


FijT.  4._Plots  2,  .'{  and  4  sliow  tho  etrint  on  the  oran^'e  trees  wlien 
too  much  fertilizer  is  used 
Plot  2  was  fertilized  with  the  standard  mixture.  Plot  :\  received  twice 
this  amount  and.  from  the  smaller  size  of  the  trees  shows  that  some  injury 
was  caused.  Plot  4  received  four  times  the  standard  mixture  and  consists 
largely  of  new  trees,  the  orijrinal  trees  heinir  practically  killed  by  the 
excessive  quantities  of  fertilizer  used.  Plot  '1  is  the  best  i)lot  of  the  forty- 
eight;  plot  3  ranked  twenty-fifth,  and  plot  4  forty-eighth. 


26 


Florida  Agricultural  Experiment  Station 


Fig.  5. — Results  of  plots  when  two  elements  in  the  standard  mixture 

were  increased. 


Bulletin  15^,  ^itrus  Fertilizer  Experiments  27 

rious  than  similar  increases  of  nitrogen  and  phosphoric  acid. 
See  Fig.  5  for  photographs  of  these  plots. 

The  mulched  plots  and  the  plots  which  received  clean  culti- 
vation the  entire  year  are  among  the  best  in  the  grove.  This 
treatment  has  been  of  benefit  in  two  ways :  by  conserving  mois- 
ture and  supplying  additional  nitrogen.  The  cultivation  thru 
the  year  has  led  to  increased  nitrification  of  the  organic  matter 
of  the  soil  thus  liberating  a  supply  of  available  nitrogen  in 
addition  to  that  supplied  in  the  fertilizer.  Determinations  on 
several  occasions  during  the  early  years  of  the  experiment  have 
shown  that  these  plots  contained  more  nitrates  in  the  soil  than 
was  found  in  the  soil  of  adjacent  plots.  The  soil  on  which  the 
plots  were  located  was  naturally  a  rather  dry  soil  so  that  the 
continuous  cultivation  and  the  mulch  of  dry  leaves  and  weeds 
have  aided  in  conserving  moisture  during  dry  periods.  Table 
10  shows  that  the  clean  culture  plots  made  more  growth  than 
any  others  during  the  early  years  of  the  experiment  but  that 
after  1913  they  did  not  do  quite  so  well.  This  would  indicate 
that  for  young  trees  continuous  clean  cultivation  is  of  benefit  in 
promoting  good  vigorous  growth,  but  after  a  few  years  it  is 
possible  to  cultivate  too  much.  Determinations  made  at  the 
end  of  the  experiment  show  that  the  soil  of  the  clean  culture 
plots  has  lost  about  18  percent  of  the  organic  matter  due  to  the 
continuous  cultivation  as  compared  with  the  soil  of  adjacent 
plots.     (See  Fig.  6  for  photograph  of  plot  46.) 

SOURCES  OF  NITROGEN 

Sulphate  of  ammonia  and  nitrate  of  soda  are  the  most  com- 
monly used  sources  of  nitrogen  for  citrus  trees.  They  are  usually 
the  least  expensive  per  pound  of  nitrogen  and  as  a  rule  have 
given  the  best  results  in  practice.  It  has  been  pointed  out  else- 
where that  the  continued  use  of  sulphate  of  ammonia  increases 
the  acidity  of  the  soil  while  nitrate  of  soda  decreases  acidity, 
and  this  opposite  tendency  of  the  two  materials  has  been  pre- 
sented as  an  argument  for  using  them  together  or  alternating 
one  with  the  other.  Additional  important  reasons  for  thus 
using  them  can  be  given.  In  the  discussion  on  soil  tanks  it  was 
pointed  out  that  the  loss  of  nitrate  of  soda  by  leaching  was  much 
greater  than  sulphate  of  ammonia,  and  that  the  losses  were 
greatest  after  heavy  rains.  In  order  to  get  the  maximum  i)enefit 
from  the  use  of  nitrate  of  soda  it  should  be  used  in  small  appli- 
cations during  the  drier  season  of  the  year.    Its  nitrogen  being 


^v*aK;i 


Fig.  6. — Plot  43,  no  fertilizer;  Plot  32,  dissolved  bone  black; 
Plot  46,  standard  and  clean  culture 
Plot  43  received  no  fertilizer  during  the  period  of  the  experiment.  It 
ranks  forty-third.  On  plot  32  dissolved  bone  black  was  used  instead  of 
acid  phosphate.  This  plot  ranked  twenty-eighth.  Plot  46  was  fertilized 
with  the  standard  mixture,  and  in  addition  was  cultivated  thru  the  entire 
year.     It  ranked  sixth  at  the  end  of  the  experiment. 


Bulletin  15^,  Citrus  Fertilizer  Experiments  29 

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Fig.  7.— This  tiguro  shows  effects  of  excessive  amounts  of  fertilizer 


30  Florida  Agricultural  Experiment  Station 

immediately  available  to  the  tree  it  is  an  excellent  material  to 
use  in  the  spring  application  of  fertilizers.  At  this  time  the 
tree  is  preparing  to  put  out  the  spring  growth  and  produce  bloom 
and  more  nitrogen  is  needed  at  this  time  than  during  any  other 
period  of  the  year.  Nitrate  of  soda  supplies  this  need  in  a  form 
which  the  trees  can  use  as  soon  as  it  is  placed  in  the  soil.  Later 
on  in  the  season  if  the  trees  have  a  yellow  color  and  show  lack 
of  nitrogen  a  light  top  dressing  of  nitrate  of  soda  will  usually 
be  of  considerable  benefit,  not  only  in  putting  the  trees  into 
healthy  growing  condition  but  in  assisting  in  the  development 
of  the  fruit.  The  only  disadvantage  likely  to  occur  in  using 
nitrate  of  soda  in  this  way  comes  when  it  is  applied  to  a  very 
dry  soil.  It  may  remain  unused  in  the  soil  for  some  time,  until 
a  rain  occurs,  making  it  at  once  available,  and  the  trees  absorb 
so  much  of  it  that  injury  results.  This  is  not  likely  to  happen  if 
small  amounts  are  used.  From  2  to  3  pounds  of  nitrate  of 
soda  to  trees  bearing  ten  boxes  of  fruit  may  be  considered  a 
rather  light  application. 

Sulphate  of  ammonia  may  be  expected  to  be  of  greater  benefit 
during  the  wet  season.  It  has  been  shown  that  this  material  is 
much  less  liable  to  be  leached  out  of  the  soil  than  nitrate  of  soda. 
Therefore,  during  the  rainy  season  its  effects  will  be  more  lasting 
and  extend  over  a  longer  period  than  nitrate  of  soda.  In  other 
words,  it  will  furnish  a  more  constant  and  uniform  supply  of 
nitrogen  during  the  wet  period.  The  ammonia  of  this  material 
becomes  available  to  the  plant  only  after  it  has  been  changed 
to  the  nitrate  form  thru  the  process  of  nitrification.  This  change 
is  brought  about  gradually  and  thus  the  effects  of  the  sulphate 
of  ammonia  are  extended  over  a  longer  period.  It  will  be  noted 
in  Table  9  that  plot  16  which  received  one-half  of  the  nitrogen 
in  the  form  of  sulphate  of  ammonia  and  the  other  half  as  nitrate 
of  soda  made  a  better  growth  than  any  plot  receiving  nitrate  of 
soda  exclusively,  thus  emphasizing  the  point  brought  out  that 
the  two  materials  used  together  will  give  better  results  than 
where  nitrate  of  soda  is  used  alone. 

ORGANIC  SOURCES  OF  NITROGEN 

Two  plots,  25  and  26,  received  steamed  bone  as  the  source  of 
phosphoric  acid  and  as  this  material  carried  a  little  over  3 
percent  ammonia  this  was  taken  into  account.  As  the  quantity 
of  steamed  bone  required  to  supply  the  proper  amount  of  phos- 
phoric acid  furnished  less  than  one-fourth  enough  nitrogen  the 
balance  was  made  up  of  sulphate  of  ammonia,  so  that  the  main 


Bulletin  154,  Citrus  Fertilizer  Experiments  31 

source  of  nitrogen  for  these  trees  was  the  latter  material.  The 
behavior  of  steamed  bone  as  a  source  of  phosphoric  acid  is 
discussed  in  the  section  on  Sources  of  Phosphoric  Acid. 

With  one  or  two  exceptions  the  plots  receiving  dried  blood  or 
cottonseed  meal  are  not  among  the  best.  Plot  47,  one  of  the 
best  in  the  experiment,  received  clean  cultivation  in  connection 
with  dried  blood,  during  the  entire  period.  It  has  already  been 
pointed  out  that  this  cultivation  was  of  marked  benefit  in  pro- 
ducing growth,  especially  during  the  early  years  of  the  experi- 
ment. On  plot  22  cottonseed  meal  was  used  in  connection  with 
sulphate  of  ammonia,  the  amount  of  the  latter  being  the  same 
as  was  used  on  plot  1  which  ranked  second  in  the  series.  While 
these  materials  have  not  brought  about  any  actual  injury  and, 
contrary  to  the  general  opinion,  have  not  produced  dieback,  this 
experiment  has  shown  that  they  should  not  be  relied  upon  as  the 
sole  source  of  nitrogen  for  citrus  trees.  Experience  has  shown 
that  an  occasional  application  of  one  or  the  other  may  be  of 
benefit  probably  in  stimulating  the  growth  of  the  beneficial  soil 
bacteria,  but  when  used  continuously  they  are  distinctly  inferior 
to  the  mineral  sources  of  nitrogen. 

SOURCES  OF  PHOSPHORIC  A(  ID 

Of  the  five  sources  of  phosphoric  acid  used,  acid  phosphate 
has  given  the  best  results.  The  eleven  best  plots  all  received 
this  material.  Steamed  bone  has  also  given  good  results,  plot 
25,  which  received  this  material,  ranking  twelfth  in  the  list. 
No  explanation  can  be  given  for  the  poor  behavior  of  dissolved 
bone  black  in  this  experiment.  As  Table  10  shows,  neither  of 
the  two  plots,  24  and  ')2,  fertilized  with  this  material,  have  ever 
ranked  above  twenty-third  during  the  ten  years  of  the  experi- 
ment. The  same  thing  may  be  said  with  regard  to  plots  27  and 
28,  fertilized  with  Thomas  slag.  These  two  plots  have  stood 
near  the  bottom  of  the  list  during  the  ten  years'  work.  The  trees 
in  both  these  plots  have  shown  evidence  of  malnutrition,  such 
as  frenching,  and  in  some  years  have  produced  but  a  small 
amount  of  new  growth.  Plot  28,  receiving  twice  as  much 
Thomas  slag  as  plot  27,  consists  on  the  average  of  somewhat 
smaller  trees,  showed  more  frenching  from  time  to  time,  ami  in 
general  showed  more  pronounced  symptoms  of  poor  nutrition 
during  the  period  of  the  experiment  than  did  plot  27. 

I SK   OF    FLOATS 

Plots  ;^,3,  'M,  :}.■)  and  'M]  were  fertilized  with  finely  ground  raw 
rock  phosphate,  connnonly  known  as  tloats.     The  formulas  used 


32  Florida  Agricultural  Experiment  Station 

were  as  follows:  Plot  33,  5-6-6,  from  sulphate  of  ammonia, 
floats  and  high  grade  sulphate  of  potash;  plot  34,  5-12-6,  from 
the  same  materials;  plot  35,  5-24-6,  from  the  same  materials; 
plot  36,  5-24-6,  from  cottonseed  meal,  floats  and  high  grade  sul- 
phate of  potash. 

At  the  end  of  the  experiment  plots  35  and  36  were  receiving 
a  quantity  of  floats  equivalent  to  a  yearly  application  of  over 
1300  pounds  per  acre.  It  will  be  noted  that  these  two  plots  made 
the  best  growth  among  the  float  plots.  In  1912  they  ranked 
third  and  seventh  respectively.  From  1913  on  they  gradually 
declined  as  compared  with  other  plots,  until  at  the  end  of  the 
experiment  in  1918  they  were  in  the  nineteenth  and  eighteenth 
places.  Plot  36  made  somewhat  more  growth  on  the  average 
than  plot  35.  The  rank  of  plot  36  from  year  to  year  is  shown 
graphically  in  Fig.  8.  It  will  be  noted  that  plot  36  was  at  its 
best  in  1913,  and  that  from  that  year  on  there  was  a  gradual 
decline  in  comparative  growth.  This  decline  may  probably  be 
attributed  to  the  inability  of  the  trees  to  obtain  sufficient  phos- 
phoric acid  from  the  floats  to  make  maximum  growth.  However, 
both  35  and  36  were  among  the  best  half  of  the  plots  at  the 
end  of  1918. 

AVAILABILITY  OF  PHOSPHATES 

The  better  results  obtained  by  the  use  of  acid  phosphate  over 
other  sources  of  phosphoric  acid,  should  in  all  probability  be 
attributed  to  its  more  ready  availability.  A  large  proportion  of 
the  phosphoric  acid  which  it  carries  is  soluble  in  water,  while 
such  materials  as  bone,  Thomas  slag  and  floats  contain  no  water- 
soluble  phosphoric  acid.  So  far  as  known  the  phosphoric  acid 
of  the  soil  is  absorbed  by  the  plant  roots  in  only  one  form,  namely, 
the  mono-calcium  phosphate,  or  the  so-called  water-soluble  form 
found  in  acid  phosphate.  This  form  contains  one  part  of  lime 
combined  with  two  parts  of  phosphoric  acid.  When  acid  phos- 
phate is  added  to  the  soil  the  mono-calcium  phosphate  combines 
with  more  lime  to  form  the  di-calcium  phosphate,  or  the  so- 
called  "reverted"  phosphate,  which  contains  two  parts  of  lime 
combined  with  two  parts  of  phosphoric  acid.  The  reverted  form 
is  fairly  soluble  in  water  containing  carbon  dioxide.  Usually 
an  additional  change  takes  place  later  on  and  the  reverted  form 
combines  with  still  more  of  the  lime  of  the  soil  and  forms  tri- 
calcium  phosphate,  containing  three  parts  of  lime  combined  with 
two  of  phosphoric  acid.  This  is  the  form  of  phosphoric  acid 
found  in  floats  and  bone. 


Bulletin  15 A,  Citrus  Fertilizer  Experiments  33 

/9/0      /9/t      /9/X      /9/3      /^/V     /9fS     /t/L     /f/7      /9f^ 


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FifT.   8. — Comparative  ^Towth  of  plots  27,  4.'?,  '-Vl,  3ti  and  -li't 


34  Florida  Agricultural  Experiment  Station 

The  thought  might  occur  that  since  acid  phosphate  after 
being  added  to  the  soil  ultimately  assumes  the  form  of  the  tri- 
calcium  phosphate,  it  would  be  reasonable  to  expect  as  good 
results  from  a  direct  application  of  the  latter  form  of  material. 
The  difference  in  availability  is  explained  by  the  fact  that  when 
acid  phosphate  is  added  to  the  soil  it  dissolves  in  the  soil  water 
and  is  soon  distributed  uniformly  and  widely  among  the  soil 
particles.  When  it  changes  to  the  reverted  form  it  remains  as 
a  thin  film  deposited  over  the  surface  of  the  particles  of  soil  and 
thus  is  in  the  best  possible  condition  to  go  into  solution  thru  the 
action  of  the  soil  water  and  to  come  into  contact  with  the  tree 
roots. 

Where  the  insoluble  phosphates  are  used  it  is  impossible  to 
obtain  as  thoro  and  uniform  a  distribution  of  the  solid  particles 
of  the  material,  even  if  very  finely  powdered,  as  it  is  in  the  case 
of  a  solution. 

The  phosphoric  acid  of  steamed  bone,  altho  in  the  form  of 
tri-calcium  phosphate,  is  more  readily  available  than  the  same 
form  as  contained  in  floats.  In  the  former  material  the  phos- 
phoric acid  is  intimately  associated  with  the  organic  material 
of  the  bone.  When  this  decays  it  acts  on  the  insoluble  phosphate 
and  makes  it  gradually  available.  Steamed  bone  has  usually 
given  excellent  results  as  a  source  both  of  nitrogen  and  of  phos- 
phoric acid,  and  while  not  as  quick  acting  as  some  other  mate- 
rials, its  effects  are  usually  more  lasting.  It  is  usually  considered 
that  about  one-half  of  the  phosphoric  acid  of  steamed  bone  be- 
comes available  the  first  season,  the  remainder  gradually  be- 
coming available  in  succeeding  years. 

SOURCES  OF  POTASH 

Of  the  six  sources  of  potash  used  in  this  experiment,  the  high 
grade  and  low  grade  sulphates  and  hard  wood  ashes  have  all  given 
excellent  results.  The  best  ten  plots  all  received  high  grade 
sulphate  of  potash.  Plot  37  to  which  low  grade  sulphate  of 
potash  was  applied,  ranked  eleventh  at  the  end  of  the  work. 
The  hard  wood  ashes  plot  ranked  fifteenth.  One  objection  to 
the  continuous  use  of  the  latter  material  has  been  brought  out 
in  this  experiment,  and  is  discussed  in  the  section  dealing  with 
lime  and  other  alkaline  materials.  The  frenched  condition  of  the 
trees  brought  on  by  the  ashes  was  not  so  severe  as  on  other  plots, 
but  was  sufficient  to  interfere  somewhat  with  normal  growth. 
An  occasional  application  of  ashes  to  citrus  trees  would  probably 


Bulletin  154,  Citrus  Fertilizer  Experiments  35 

give  very  little  if  any  trouble.  The  muriate  and  the  nitrate  of 
potash  gave  only  fair  results.  The  trees  on  these  two  plots  did 
not  produce  quite  the  thrifty,  vigorous  growth  characteristic  of 
the  best  plots. 

The  trees  in  plot  40,  which  received  kainit  as  the  source  of 
potash,  made  very  poor  growth  during  the  entire  period  of  the 
experiment.  Compared  with  plots  receiving  the  high  and  low 
grade  sulphate  and  ashes,  they  were  smaller  in  size,  growth  was 
less  abundant,  and  appeared  much  less  thrifty  and  vigorous. 
This  plot  received  the  same  treatment  as  plot  41  in  the  next  row, 
excepting  the  source  of  potash,  but  the  trees  were  not  more 
than  two-thirds  the  size  of  those  in  plot  41. 

SOIL  ACIDITY 

Table  11  gives  the  lime  requirement  of  the  various  plots  for 
four  different  dates,  samples  of  soil  being  taken  in  March,  July, 
and  December  of  1913  and  in  July,  1915.  By  the  term  "lime 
requirement"  is  meant  the  amount  of  lime  necessary  to  be  added 
to  the  soil  to  bring  about  an  alkaline  reaction.  In  the  method  used 
the  soil  is  treated  with  varying  quantities  of  lime  water  of 
standard  strength  until  the  proper  amount  necessary  to  give  an 
alkaline  reaction  is  reached.  The  figures  in  the  table  represent 
pounds  of  calcium  carbonate  (ground  limestone)  per  acre. 
Samples  of  soil  were  taken  from  the  plots  where  the  fertilizers 
had  been  applied  and  also  in  the  middle  of  the  tree  rows  where 
the  soil  had  never  been  fertilized.  The  difference  between  the 
lime  requirement  of  any  plot  and  the  corresponding  middle  would 
show  the  effect  of  the  fertilizer  used  on  the  plot  in  increasing  or 
decreasing  the  acidity  of  the  soil.  It  will  be  noted  from  the 
table  that  plots  11,  12,  21  and  39,  receiving  ground  limestone, 
and  plot  30,  receiving  hardwood  ashes,  all  show  an  alkaline 
reaction,  due  to  the  effect  of  these  basic  materials  in  neutralizing 
the  acidity  originally  present  and  also  that  which  may  have  de- 
veloped from  time  to  time.  Plots  27  and  28,  receiving  basic  slag 
and  nitrate  of  soda,  show  a  marked  decrease  in  lime  require- 
ment as  compared  with  the  corresponding  checks.  Basic  slag 
has  an  alkaline  reaction  and  contains  usually  a  small  excess  of 
lime  over  and  above  that  in  combination  with  the  phosphoric 
acid  in  it.  This  excess  of  lime  is  seldom  over  5  to  10  percent. 
Hence,  basic  slag  in  the  amounts  ordinarily  applied  in  practice 
would  not  supply  sullicicnt  lime  to  neutralize  the  acid  condition 
of  a  sour  soil  except  in  a  limited  degree  as  is  here  shown.     The 


36 


Florida  Agricultural  Experiment  Station 


TABLE   11. — Lime  Requirement.    Pounds  per  Acre,  9  Inches 


Plot  No. 


March,  1913    ,     July,  1913 


Dec,  1913 


July,  1915 


Plot 

Middle 

Plot 

Middle 

Plot 

Middle 

Plot 

Middle 

1 

1600 

1070 

2140 

1070 

1600 

1070 

2140 

2140 

2 

2670 

1600 

3210 

2670 

3210 

1600 

3740 

2670 

3 

2670 

1070 

2210 

2670 

3210 

2140 

4810 

2140 

4 

3210 

1070 

3740 

2140 

2670 

2140 

4810 

1600 

5 

2670 

1070 

3740 

2140 

3740 

2140 

5350 

1600 

6 

4280 

1070 

3740 

2670 

3740 

2140 

4810 

2140 

7 

2670 

1600 

3740 

2670 

3210 

1600 

3740 

2670 

8 

2670 

1070 

3210 

1070 

2140 

1070 

3740 

2140 

9 

2670 

1070 

3210 

2140 

2140 

1600 

2670 

1600 

10 

2670 

2140 

3210 

2670 

3210 

2140 

3210 

3210 

11 

Alk.* 

2670 

Alk.* 

3210 

Alk.* 

3210 

Alk.* 

2670 

12 

Alk.* 

2670 

.  Alk.* 

3210 

Alk.* 

3210 

Alk.* 

4280 

13 

3740 

2670 

4280 

3210 

4280 

3210 

4810 

4280 

14 

2670 

2670 

3740 

3210 

3740 

3210 

4810 

2670 

15 

2670 

2140 

3740 

2670 

2670 

2140 

2670 

3210 

16 

2670 

1070 

2140 

2140 

2670 

1600 

3740 

1600 

17 

2670 

2670 

3210 

3210 

3210 

2670 

4810 

3210 

18 

2670 

2670 

3740 

4810 

2670 

2670 

4280 

2670 

19 

2670 

2140 

4280 

3210 

2140 

2670 

4280 

3740 

20 

2670 

2670 

3740 

4280 

2670 

2670 

3740 

3210 

21 

Alk.* 

2670 

Alk.* 

4280 

Alk.* 

2670 

Alk.* 

3210 

22 

2670 

2140 

5350 

3210 

4280 

2670 

4280 

3740 

23 

2670 

2670 

4810 

4810 

2670 

2670 

5350 

2670 

24 

2670 

2670 

5890 

3210 

3740 

2670 

4280 

3210 

25 

2670 

2670 

3740 

3740 

2670 

2670 

3210 

3210 

26 

2140 

2670 

4810 

2670 

3210 

2670 

3210 

2670 

27 

1600 

2140 

2140 

3740 

2140 

2140 

1600 

2140 

28 

1070 

2670 

3210 

3740 

1070 

2670 

2140 

5350 

29 

2670 

2670 

4810 

3740 

4280 

2670 

4810 

5350 

30 

Alk.* 

2140 

Alk.* 

3740 

Alk.* 

2140 

Alk.* 

2140 

31 

3210 

2670 

4810 

2670 

3210 

2670 

4810 

2670 

32 

3210 

2670 

4810 

3740 

3210 

2670 

4280 

3210 

33 

2140 

3210 

3740 

2670 

2670 

2140 

3740 

3210 

34 

2140 

2140 

4280 

3210 

2670 

2670 

3740 

3210 

35 

2140 

2670 

4280 

3210 

3740 

2670 

5350 

3740 

36 

2670 

2140 

4280 

4280 

3210 

2140 

3740 

2670 

37 

3740 

2140 

4810 

4280 

2670 

2140 

5350 

2670 

38 

3210 

2670 

4280 

3210 

3740 

2670 

4280 

3740 

39 

Alk.* 

2140 

Alk.* 

3210 

Alk.* 

2670 

Alk.* 

3210 

40 

3210 

3210 

4810 

2670 

2670 

2140 

3740 

3210 

41 

2670 

2140 

3740 

2670 

2670 

1600 

3740 

2670 

42 

2140 

2140 

3740 

2140 

2140 

1600 

2670 

2140 

43 

2140 

2670 

3740 

2670 

2140 

2140 

3210 

4280 

44 

4280 

2140 

5350 

6420 

3740 

3740 

5350 

4280 

45 

4280 

2140 

7490 

6420 

5890 

3740 

6960 

4280 

46 

3210 

2670 

4280 

2670 

3740 

2140 

3740 

4280 

47 

2670 

2140 

3740 

2140 

3210 

1600 

2670 

2140 

48 

2140 

2140 

3210 

2670 

2140 

1600 

3210 

2670 

*Alkalir 

e. 

neutralizing  effect  shown  in  these  two  plots  is  also  influenced 
by  the  nitrate  of  soda  used  in  connection  with  the  basic  slag. 
Nitrate  of  soda  also  has  an  alkaline  reaction  in  the  soil  due  to 
the  fact  that  the  N03  or  nitrate  part  of  the  material  is  used 
up  by  the  tree  much  faster  than  the  NA  or  sodium  portion. 


Bulletin  154,  Citrus  Fertilizer  Experiments  37 

This  leads  to  more  or  less  of  an  accumulation  in  the  soil  of  the 
sodium  element,  which  by  combining  with  the  carbonic  acid 
gas  of  the  soil  water  forms  carbonate  of  soda,  a  material  having 
an  alkaline  reaction. 

The  effect  of  nitrate  of  soda  on  an  acid  soil  is  also  brought 
out  by  a  study  of  the  lime  requirement  of  plots  15  and  48  which 
received  this  material  as  the  source  of  nitrogen.  In  both  plots 
the  tendency  of  the  nitrate  of  soda  to  decrease  acidity  is  clearly 
shown.  In  plot  15  there  is  an  actual  decrease  in  the  acid  condi- 
tion of  the  soil,  while  in  plot  48  the  soda  has  at  least  prevented  an 
increase.  In  the  soil  of  plot  42,  receiving  nitrate  of  potash  and 
nitrate  of  soda,  the  tendency  also  is  for  the  acidity  to  decrease. 

ACID  FERTILIZERS 

The  well  known  tendency  of  sulphate  of  ammonia  to  increase 
the  acid  condition  of  the  soil  is  shown  here  in  the  majority  of 
the  plots  receiving  this  material  as  the  source  of  nitrogen.  The 
plots  showing  the  highest  degree  of  acidity  nearly  all  receive 
this  material.  It  is  true  that  some  form  of  phosphoric  acid  and 
of  potash  were  used  on  each  plot  in  connection  with  the  sulphate 
of  ammonia  and  it  might  be  argued  that  these  materials  were  in 
part  responsible  for  the  acid  condition  present.  The  work  of 
other  investigators,  however,  where  sulphate  of  ammonia  was 
used  alone,  has  shown  that  this  material  must  be  held  as  the 
chief  cause  of  acidity.  The  absorption  and  nitrification  of  the 
ammonia  of  this  material  is  comparatively  rapid,  being  followed 
by  its  final  utilization  by  the  tree.  This  leaves  the  sulphuric  acid 
portion  in  the  soil,  thus  bringing  about  acid  conditions.  The 
potash  of  the  muriate  and  sulphate  of  potash  disappears  much 
more  slowly  from  the  soil  as  the  latter  has  the  power  of  retaining 
for  some  considerable  time  the  potash  or  basic  element  of  these 
materials.  Therefore,  while  the  tendency  of  these  materials 
would  be  to  produce  in  the  long  run  an  acid  condition,  their  action 
would  be  much  slower  than  sulphate  of  ammonia.  Similarly,  it 
has  been  shown  that  the  continuous  use  of  acid  phosphate  does 
not  increase  acidity.  On  the  contrary,  it  seems  to  decrease  some- 
what the  acidity  already  present  in  the  soil.  The  figures  in 
Table  11  for  the  plots  receiving  floats  or  raw  rock  i)hosphato 
are  not  very  conclusive.  In  three  plots  out  of  four  sulphate  of 
ammonia  was  used  with  the  floats  so  that  the  influence  of  the 
latter  on  the  acidity  of  the  soil  would  be  over-shadowed  by  that 
of  the  sulphate  of  ammonia.  In  general,  however,  it  may  be  said 
that  the  use  of  floats  would  have  a  tendency   to  decrease  the 

2i o 1 85 


88  Florida  Agricultural  Experiment  Station 

acidity  of  the  soil.  The  various  forms  of  raw  rock  phosphate 
on  the  market  contain  more  or  less  carbonate  of  lime  as  an 
impurity  and  their  influence  on  the  acid  condition  of  the  soil 
would  be  proportional  to  the  amount  of  this  material  present. 

EFFECT  OF  ACIDITY  ON  GROWTH 

So  far  as  could  be  noted  an  acid  soil  has  no  injurious  effect 
on  the  growth  of  the  orange  tree.  On  some  of  the  most  acid 
plots  in  the  grove  the  trees  are  vigorous  and  have  made  very  good 
growth  ranking  well  up  among  the  best  plots  in  the  grove.  These 
experiments  would  seem  to  show  that  so  far  as  growth  is  con- 
cerned the  citrus  tree  is  very  little  influenced  by  an  acid  condition 
of  the  soil.  Where  a  leguminous  cover  crop  is  desired  during  the 
rainy  season  the  situation  is  different.  During  the  early  years  of 
the  experiment  a  beggarweed  cover  crop  was  allowed  to  occupy 
the  soil  during  the  summer  months.  After  a  time  the  soil  became 
so  acid  that  a  fair  stand  could  not  be  obtained  and  cowpeas  and 
velvet  beans  were  used  instead.  These  crops  appear  to  be  much 
less  susceptible  to  acidity  than  beggarweed  and  will  do  fairly 
well  on  soils  on  which  the  beggarweed  almost  refuses  to  grow. 
A  study  of  Table  11  brings  out  the  interesting  fact  that  the 
acidity  varies  with  the  season,  being  greater  in  summer  than  in 
winter.  The  average  number  of  pounds  per  acre  of  carbonate  of 
lime  required  for  the  plots  receiving  the  standard  mixture  of 
sulphate  of  ammonia,  acid  phosphate  and  high  grade  sulphate  of 
potash  is  4360  for  the  summer  months  and  3050  for  the  winter 
months,  a  difference  of  over  half  a  ton.  A  probable  explanation 
of  this  fact  is  that  during  the  summer  months  the  high  tem- 
peratures and  abundant  rainfall  lead  to  more  rapid  chemical  and 
biological  changes  in  the  soil.  This  brings  about  greater  decay 
of  organic  matter  and  more  rapid  transformations  in  the  fertiliz- 
ing materials  present,  resulting  in  a  more  rapid  formation  of 
acids. 

NATURE  OF  SOIL  ACIDITY 

Soils  may  become  acid  or  sour  (1)  thru  an  accumulation  of 
organic  acids  produced  in  the  decay  of  vegetable  matter;  (2) 
thru  the  depletion  of  the  alkaline  or  basic  constituents  of  the 
soil;  (3)  thru  the  addition  of  fertilizers  leaving  an  acid  residue 
in  the  soil.  Most  muck  and  peat  soils  are  acid  in  character  before 
being  brought  into  cultivation.  This  is  also  true  of  many  virgin 
soils  of  a  more  sandy  nature.  The  decay  of  the  vegetable  matter 
present  in  such  soils  leads  to  the  formation  of  organic  acids, 
which  tend  to  accumulate,  especially  if  these  soils  are  naturally 


Bulletin  154-,  Citrus  Fertilizer  Experiments  39 

deficient  in  lime  or  if  they  are  ill  drained.  After  such  soils  are 
cleared,  drained  and  brought  under  cultivation  this  acid  condi- 
tion disappears  to  a  considerable  extent,  due  to  the  aeration  or 
introduction  of  oxygen  into  the  soil  thru  cultural  treatment. 
Where  a  crop  of  green  material  is  turned  under,  as  in  the  prac- 
tice of  green  manuring,  the  soil  may  become  acid  for  a  time 
due  to  the  formation  of  organic  acids  in  the  decay  of  the  vege- 
table matter  plowed  under.  In  any  case  where  acids  are  formed 
they  lead  to  a  depletion  of  the  lime  of  the  soil.  It  might  be  said 
that  all  soils  tend  to  become  acid  in  time  due  to  the  removal  of 
lime  and  other  basic  materials  in  the  drainage  water.  Both  the 
lime  in  carbonate  of  lime  and  that  in  certain  silicate  compounds 
present  in  soils  are  dissolved  by  the  soil  acids  and  are  leached 
out.  When  these  forms  of  lime  finally  disappear  from  the  soil  an 
acid  condition,  so  far  as  plant  growth  is  concerned,  is  produced. 
An  application  of  lime  in  some  form  is  required  to  bring  back 
the  alkaline  reaction.  Florida  high  pine  and  flat  woods  soils, 
as  a  general  rule,  contain  relatively  small  quantities  of  lime 
(usually  very  little  if  any  in  the  carbonate  form) ,  yet  the  amount 
of  this  material  appearing  in  the  drainage  water  is  surprising. 
In  experiments  carried  out  by  the  Florida  Experiment  Station 
it  has  been  found  that  in  the  course  of  10  months  lime  equivalent 
to  250  pounds  of  calcium  carbonate  has  leached  out  and  appeared 
in  the  drainage  water  from  an  acre  of  land.  Such  a  loss  of  lime 
if  continued  for  a  few  years  would  bring  about  acid  conditions 
in  the  soil. 

The  use  of  fertilizers  such  as  sulphate  of  ammonia,  which 
leave  an  acid  residue  in  the  soil,  is  a  frequent  cause  of  soil 
acidity  under  Florida  conditions.  The  acid  residue  combines 
with  the  lime  of  the  soil  and  changes  it  to  a  soluble  form  which 
readily  leaches  out.  In  studying  the  loss  of  lime  where  different 
sources  of  ammonia  were  applied  to  the  soil,  the  Experiment 
Station  has  found  that  where  sulphate  of  ammonia  was  used 
the  loss  was  over  two  times  as  much  as  where  nitrate  of  soda 
was  used.  This  tendency  of  nitrate  of  soda  to  decrease  acidity, 
in  other  words,  to  conserve  the  lime  of  the  soil,  has  already  been 
mentioned  in  connection  with  the  discussion  of  the  loss  of  ferti- 
lizers by  leaching. 

An  important  feature  in  the  use  of  these  two  materials  is 
thus  brought  out.  It  is  an  advantage  to  use  them  together  or 
alternately,  as,  for  example,  nitrate  of  soda  as  the  source  of 
ammonia  in  the  spring  and  sulphate  of  ammonia  in  the  summer. 


Fig.  9. — Phosphate  plots 
Plots  27  and  28  were  fertilized  with  Thomas  slag  instead  of  acid  phos- 
phate. The  source  of  nitrogen  was  nitrate  of  soda.  Plot  28  received  twice 
as  much  slag  as  plot  27.  The  trees  in  both  these  plots  showed  considerable 
frenching,  plot  28  being  much  more  severely  affected.  Most  of  the  trees 
in  plot  28  show  the  type  of  growth  usually  characteristic  of  badly  frenched 
trees.  Plot  36  received  its  phosphoric  acid  in  the  form  of  floats,  four  times 
the  standard  amount  or  24  percent  being  used  in  the  mixture.  At  the  end  of 
the  experiment  this  plot  ranked  eighteenth.  Plot  27  ranked  thirty-fifth  and 
plot  28  ranked  forty-fourth. 


Bulletin  154,  Citrus  Fertilizer  Experiments  41 

Thus  the  nitrate  of  soda  would  counteract  the  acid  condition 
brought  about  by  the  sulphate  of  ammonia.  Other  and  greater 
advantages  in  thus  using  the  two  materials  are  discussed  else- 
where. 

UME  AND  OTHER  ALKALINE  MATERIALS 

Lime  and  other  alkaline  materials  \ised  in  this  experiment  have 
proven  distinctly  injurious  to  growth.  This  injury  consisted, 
in  its  .mildest  form,  of  a  light  attack  of  frenching;  in  the  severest 
type,  of  chronic,  severe  frenching,  partial  defoliation,  and 
a  permanent  retarding  of  growth,  resulting  in  stunted  under- 
sized and  unhealthy  trees.  The  alkaline  materials  and  the  ferti- 
lizers used  in  connection  with  the  plots  were  as  follows: 

Plot  11,  5-6-6,  from  sulphate  of  ammonia,  acid  phosphate,  high 
grade  sulphate  of  potash;  ground  limestone,  10  pounds  per  tree. 

Plot  12,  5-6-6,  same  fertilizer  treatment  as  plot  11,  with  lime- 
stone replaced  by  air-slaked  lime,  5  pounds  per  tree. 

Plot  21,  5-6-6,  from  cottonseed  meal,  acid  phosphate,  high- 
grade  sulphate  of  potash ;  ground  limestone,  10  pounds  per  tree. 

Plot  27,  5-6-6,  from  nitrate  of  soda,  Thomas  slag,  high-grade 
sulphate  of  potash. 

Plot  28,  5-12-6,  from  same  materials  as  plot  27. 

Plot  30,  5-6-6,  from  nitrate  of  soda,  acid  phosphate,  hard  wood 
ashes. 

Plot  39,  5-6-6,  same  treatment  as  plot  11. 

The  ground  limestone  and  air-slaked  lime  were  applied  in  the 
spring  about  two  months  after  the  spring  application  of  ferti- 
lizers, and  were  distributed  about  the  tree  to  about  the  same 
distance  from  the  trunk  as  the  fertilizers.  The  slag  and  hard- 
wood ashes  were  applied  mixed  with  the  other  fertilizers.  The 
limestone  and  air-slaked  lime  were  applied  every  year,  beginning 
with  1909,  until  1913,  when  the  injury  produced  became  quite 
noticeable  and  their  use  was  discontinued  for  the  remainder  of 
the  period  of  the  experiment.  The  slag  and  ashes  were  used 
during  the  entire  ten  years. 

During  the  early  years  of  the  experiment  considerable  french- 
ing was  found  in  all  parts  of  the  grove.  As  the  trees  suffered 
from  dieback  during  these  years  the  frenching  was  attributed  to 
the  same  causes  which  produced  the  former  disease.  In  1913  it 
was  noticed  that  the  trees  on  some  of  the  plots  receiving  alkaline 
materials  were  more  severely  frenched  than  the  remainder  of 
the  grove.   The  worst  injury  was  found  on  the  ground  limestone 


Fig.  10. — Plots  11,  12  and  21,  on  which  lime  was  used 
The  plots  illustrated  here  were  treated  with  lime  in  addition  to  the 
fertiliser.  Plot  11  received  the  standard  fertilizer  mixture  and  ground 
limestone.  Plot  21  received  the  standard  mixture  with  the  sulphate  of  am- 
monia replaced  by  cottonseed  meal  and  ground  limestone  in  addition.  This 
plot  showed  much  more  frenching  than  plot  11.  Plot  12  was  fertilized  with 
the  standard  mixture  and  air-slaked  lime  in  addition.  The  trees  showed 
very  little  frenching. 


Bulletin  15^,  Citrus  Fertilizer  Experiments  43 

plots  and  on  the  plot  receiving  a  double  quantity  of  slag.  The 
trees  on  the  air-slaked  lime  plot  and  on  the  ashes  plot  also  showed 
considerable  frenching,  which,  however,  almost  completely  dis- 
appeared after  1915,  while  the  trees  on  the  limestone  and  slag 
plots  developed  the  more  severe  symptoms  of  the  disease,  such  as 
the  narrow  pointed  leaves,  partial  defoliation,  and  general  un- 
thrifty appearance.  The  disease  continued  to  manifest  itself 
in  this  aggravated  form  in  these  particular  plots,  until  the  clos- 
ing out  of  the  experiment.  It  seriously  interfered  with  normal 
growth,  the  trees  on  the  most  severely  affected  plots  appearing 
stunted,  undersized  and  unhealthy. 

Photographs  of  plots  11,  12,  21,  27  and  28  are  reproduced  in 
Figs.  9  and  10. 

For  a  more  detailed  discussion  of  the  injury  induced  by  ground 
limestone,  the  reader  is  referred  to  Fla.  Exp.  Sta.  Bulletin  No. 
137,  Injury  to  Citrus  Trees  by  Ground  Limestone,  by  B.  F.  Floyd. 

DIEBACK  IN  THE  GROVE 

In  July,  1910,  eighteen  months  after  they  had  been  set  out, 
it  was  noticed  that  many  of  the  trees  exhibited  the  early  stages 
of  the  disease  known  as  dieback.  At  this  time  the  symptoms 
were  mainly  the  presence  of  gum  pockets  and  the  S-shaped 
branching.  An  examination  showed  about  78  percent  of  the 
trees  thus  affected.  At  the  same  time  the  trees  presented  a 
generally  unhealthy  appearance,  much  of  the  growth  coming 
from  the  lower  parts  of  the  tree  and  from  suckers.  No  measures 
for  combatting  the  disease  were  adopted  at  this  time,  since  it 
was  considered  very  undesirable  to  introduce  such  complications 
in  the  experiment  unless  absolutely  necessary.  The  grove  was 
thoroly  examined  again  in  March,  1911,  and  in  the  fall  of  that 
year  when  it  was  evident  that  the  disease  had  gained  much 
headway  and  was  causing  serious  damage.  Table  12  shows  the 
extent  to  which  the  grove  was  affected  with  the  disease.  In  this 
table  the  number  of  the  plot  and  the  fertilizer  treatment  is 
given,  in  column  I  the  number  of  trees  in  each  plot  showing 
symptoms  of  dieback  in  July  1910;  in  column  II  those  showing 
symptoms  in  March  1911,  and  in  column  111  those  developing 
the  symptoms  in  the  growth  made  in  the  spring  of  1911.  (The 
writer  is  indebted  to  B.  F,  Floyd.  Plant  Physiologist,  for  this 
table.) 

RELATION  OF  DISEASE  TO  I  EKTIMZEK 

The  use  of  organic  nitrogenous  fertilizers  has  usually  been 
regarded  as  a  cause  of  dieback.     A  study  of  Table  12  however. 


TABLE  12. — Trees  Affected  by  Dieback 
Fertilizers  Applied 


^ Different  amounts 

Half  the   startdard.„ ....: ..:.... 


II 


Standard  - ..^ — :...- — _ 

Double   the   standard 

Four  times  the  standard ..'. 

Phosphoric  acid  and  ammonia  increased  by  one-half.... 

Phosphoric  acid  and  potash  increased  by  one-half 

Ammonia  and  potash  increased  by  one-half 

Phosphoric  acid  and  potash  decreased  by  one-half 

Phosphoric  acid  and  ammonia  decreased  by  one-half.... 

Ammonia  and  potash  decreased  by  one-half 

Standard  and  finely  ground  limestone 

Standard  and  air-slacked  lime , _ , 

Standard  and  mulch 

Standard 


4 
2 
6 
9 
9 
8 
10 
9 
9 
9 
7 
9 
7 
8 


8 
4 
9 
g 
8 
9 
8 

10 

10 
7 

10 
9 
7 

10 


Nitrogen  from  different  sources 

From  nitrate  of  soda 1 

Half  from  nitrate  of  soda,  and  half  from  sulphate  of 

ammonia 

From  dried  blood 

Half  from  sulphate  of  ammonia,  and  half  from  dried 

blood    

Half  from  nitrate  of  soda,  and  half  from  dried  blood.. 

From  cottonseed  meal 

From  cottonseed  meal.   (With  ground  limestone.) 

Half  from  cottonseed  meal,  and  half  from  sulphate  of 

ammonia   

Half  from  cottonseed  meal,  and  half  from  nitrate  of 

soda    


9 

8 

9 

7 
4 
6 

8 

10 


Phosphoric  acid  from  different  sources 

From  dissolved  bone  black 

From   steamed  bone 

From  steamed  bone.  (Double  amount.) 

From  Thomas'  slag.  (Nitrogen  from  nitrate  of  soda.).. 
From  Thomas'  slag.  (Double  amount.   Nitrogen  from 

nitrate  of  soda.) 

From  acid  phosphate.   (Potash,  7%  percent  in  June, 

7%  percent  in  October  and  3  percent  in  February.) 
From  acid  phosphate.  (Nitrogen  from  nitrate  of  soda. 

Potash  from  hardwood  ashes.) 

From  acid  phosphate.  (Standard.) 

From   dissolved   boneblack 

From   floats ., 

From  floats.   (Double  amount.) 

From  floats.   (Four  times  amount.) 

From   floats.    (Four  times   amount.     Nitrogen  from 

cottonseed    meal.) 


7 

10 

9 

8 


4 
10 

8 
10 

9 

9 


10 

9 

10 

8 


4 
10 

9 

10 
10 
10 

10 


Potash  from  different  sources 

From  low-grade  sulphate 

From  muriate 

From  high-grade  sulphate.   (With  ground  limestone.) 

From  kainit 

From  high-grade  sulphate.   (Standard.) 

From  nitrate  of  potash.    (Balance  of  nitrogen  from 
nitrate   of    soda.) 


9 

9 

10 

6 

7 


9 

8 

10 

10 

9 


Different  culture,  etc. 

No   fertilizer 

Standard  

Standard   and   mulch 

Standard  and  clean  culture 

Nitrogen  from  dried  blood.    Clean  culture 

Nitrogen  from  nitrate  of  soda.    Clean  culture. 


3 

7 
8 
10 
9 
7 


4 
10 

8 
10 
10 

6 


Total  number  of  trees  affected  with  dieback |373   |411f241 


Bulletin  154,  Citrus  Fertilizer  Experiments  45 

brings  out  the  fact  that  in  this  instance  plots  receiving  a  strictly 
mineral  fertilizer  were  as  badly  affected  with  the  disease  as 
were  those  receiving  cottonseed  meal,  dried  blood  and  other 
organic  sources  of  nitrogen.  At  no  time  during  the  progress 
of  the  disease  could  any  definite  relation  be  established  between 
the  disease  and  any  particular  fertilizer.  In  other  words,  the 
disease  appeared  to  be  entirely  independent  of  the  fertilizers 
used.  It  has  been  mentioned  elsewhere  that  when  they  were  set 
out  three-fourths  of  a  pound  of  steamed  bone  meal  was  used 
under  each  tree.  It  is  possible  that  the  organic  nitrogen  in  the 
bone  meal  may  have  been  the  primary  cause  of  the  disease,  but 
as  every  tree  in  the  grove  was  treated  in  this  way  this  theory  was 
impossible  of  proof. 

TREATMENT  OF   DIEBACK 

In  the  spring  of  1912  the  disease  had  reached  a  serious  stage 
and  it  became  evident  that  measures  for  combatting  it  must  be 
taken.  The  more  advanced  symptoms,  such  as  bark  excrescences, 
stained  terminal  branches,  and  multiple  buds,  were  quite  abun- 
dant, and  a  few  trees  were  in  such  bad  condition  that  it  was 
necessary  to  replace  them  with  others.  The  fertilizer  applica- 
tions for  the  spring  and  summer  of  1912  were  omitted  and  the 
trees  were  sprayed  with  Bordeaux  mixture  in  February  and 
April.  In  order  to  get  at  the  effect  of  this  spray  in  controlling 
the  disease,  the  fifth  tree  in  every  plot  was  left  unsprayed  as  a 
check.  In  the  latter  part  of  the  year  it  was  evident  that  the 
disease  was  much  less  prevalent  than  before  the  treatment.  In 
January,  1913,  B.  F.  Floyd  made  a  careful  examination  of  the 

TABLE   13. — DiEBACK  on  Experimkntal  Plots  in  January.  1913 


c 

01 

-■J 

-a 
3 

a; 

a; 
o 
■J. 

o 

^ 

c  S 

^  u 

'■Z 

c^ 

52 

"5 

£2 

O 

72  a: 

CSK 

^. 

<i^ 

Affected      trees      amonj? 

sprayed  

111 

20 

10 

0 

4 

Affected  trees  among  un-     , 

sprayed  

'       27 

i        15        1 

13 

1 

!      1 

Percentage  affected  trees 

1 

among  sprayed  

25.7 

4.6 

2.3 

0 

1         0.93 

Percentage  affected  trees 

among   unsprayed    

56.2 

,       31.3 

27.1 

2.1 

2.1 

Total    number    trees    af- 

1 

fected    

138 

35 

23 

1 

5 

46  Florida  Agricultural  Experiment  Station 

trees  for  symptoms  of  dieback.  Table  13  summarizes  his  notes 
made  at  that  time.  This  table  shows  that  over  56  percent  of  the 
unsprayed  trees  still  showed  dieback  in  the  gum  pocket  stage  as 
compared  with  25.7  percent  of  the  sprayed  trees.  While  a  total 
of  138  trees  showed  this  symptom,  none  were  at  all  severely 
affected  or  were  being  injured  by  the  disease.  The  superficial 
symptoms  such  as  stained  terminal  branches,  bark  excrescences 
and  multiple  buds,  were  quite  scarce.  It  will  be  noted  that  in 
November,  1911,  81.7  percent  of  the  trees  showed  gum  pockets, 
while  in  January,  1913,  the  unsprayed  trees  showed  56.2  percent 
affected.  This  indicates  a  decrease  in  the  disease  during  this 
period  from  causes  other  than  the  spray  treatment.  Probably 
the  omission  of  the  fertilizer  application  or  other  natural  causes 
were  of  influence  here  in  bringing  about  a  decrease  in  the  disease. 
Nevertheless  it  may  be  concluded  from  the  data  given  that  the 
Bordeaux  treatment  was  quite  effective  in  this  instance  in  the 
control  of  dieback.  In  June,  1913,  the  trees  appeared  to  be 
practically  free  from  the  disease,  but  in  June,  1915,  slight  indi- 
cations of  it  were  again  noted.  Gum  pockets  were  found  on  the 
new  growth  on  52  trees.  They  were  not  numerous  on  any  of 
the  trees,  in  most  cases  a  careful  search  being  necessary  to  find 
them.  Of  the  52  trees  affected,  28  were  the  fifth  tree  in  the 
plot,  trees  which  had  been  left  unsprayed  at  the  time  of  treatment 
with  Bordeaux  mixture.  No  further  treatment  was  given  at  this 
time  and  the  symptoms  of  the  disease  disappeared  from  natural 
causes  later  in  the  year.  From  the  end  of  the  year  1915  on  to 
the  close  of  the  experiment,  no  further  trouble  was  experienced 
with  the  disease. 

FREEZE  OF  1917 

During  the  first  week  of  February,  1917,  a  cold  wave  swept 
over  the  state  bringing  freezing  temperatures,  especially  on  the 
3rd  and  4th,  and  causing  considerable  damage  to  the  citrus  and 
truck  industries. 

In  the  experimental  grove  temperatures  of  21  on  the  3rd,  and 
22  on  the  4th  were  noted.  A  reproduction  of  the  air  and  soil 
temperature  records  for  the  grove  for  the  week  ending  February 
5  is  given  in  Fig.  11.  In  order  to  ascertain  the  extent  and 
nature  of  the  cold  injury  the  grove  was  carefully  examined  dur- 
ing the  first  week  of  March.  It  was  particularly  desired  to  find 
out  what  effect,  if  any,  the  various  fertilizer  treatment  had  in 
making  the  trees  more  or  less  resistant  to  cold  injury.     The 


Bulletin  154,  Citrus  Fertilizer  Experiments 


47 


criteria  used  in  this  study  were  the  amount  of  defoliation,  the 
number  of  twigs  killed  back  and  the  distance  to  which  they  were 
killed,  and  the  amount  and  character  of  the  new  growth  produced 
after  the  freeze. 

The  individual  plots  showed  considerable  variation  in  the 
amount  of  injury  caused  by  the  cold,  plots  28,  5,  7,  27,  21,  43  and 
39  being  the  most  seriously  injured.  At  the  time  of  the  freeze 
the  trees  in  these  plots  were  in  a  weakened  and  unthrifty  condi- 
tion, owing  to  various  causes,  such  as  over-fertilization  and  the 
effect  of  alkaline  materials,  discussed  in  detail  elsewhere.  The 
fact  that  they  were  unthrifty  was  undoubtedly  the  cause  of  their 
more  serious  injury  from  cold.  It  is  difficult  to  express  the 
degree  of  injury  in  definite  figures,  but  these  trees  showed  ap- 
proximately 85  percent  defoliation,  with  70  percent  of  the  twigs 
killed  back  on  the  average  about  9  inches.  The  new  growth 
which  was  coming  out  was  rather  scanty  and  was  weak  in 
character. 


Fijr.   11. — Roprodui'tion  of  air  and  soil  tomperaturo  rciorcis  for  tlie  lirove 
(lurinjr  the  free/.t"  of   Ft-bruary.   liH7 

These  ligures  may  be  compared  with  similar  ones  lor  plots 
showing  the  least  amount  of  injury.  Plots  2.  1,  47.  4S,  12,  13 
and  IG  were  selected  for  this  comparison.  These  trees  averaged 
approximately  65  percent  defoliation  with  30  percent  of  the 
twigs  killed  back  a  distance  of  about  5  inches.  The  new  growth 
coming  out  was  considerably  more  abundant  and  more  thrifty 


48  Florida  Agricultural  Experiment  Station 

than  on  the  other  plots.  These  figures  show  that  trees  in  good 
healthy  condition  are  more  able  to  withstand  a  freeze  than  are 
those  in  an  unthrifty  condition,  and  that  the  former  make  a 
quicker  recovery.  This  statement  was  borne  out  by  the  general 
appearance  of  the  trees  and  their  subsequent  behavior.  No  con- 1 
elusive  evidence  could  be  obtained  indicating  that  any  special! 
fertilizer  treatment  among  those  used  on  the  better  plots  was 
more  effective  than  another  in  making  the  trees  resistant  to| 
frost. 

CONCLUSIONS 

1.  In  this  experiment  sulphate  of  ammonia,  acid  phosphate,! 
and  high-grade  sulphate  of  potash  gave  somewhat  better! 
results  as  measured  by  increase  in  growth,  than  any  other] 
mixture. 

2.  Good  results  were  obtained  from  the  use  of  nitrate  of  sodaj 
as  a  source  of  ammonia,  from  steamed  bone  and  floats  asj 
sources  of  phosphoric  acid,  and  from  the  low-grade  sulphate^ 
hardwood  ashes  and  the  muriate,  as  sources  of  potash. 

3.  The  use  of  ground  limestone  and  Thomas  slag  have  causec 
injury,  indicated  by  frenching. 

4.  Clean  cultivation  thruout  the  year  was  of  considerable  benefil 
to  young  trees,  but  after  a  few  years  leads  to  a  loss  of  soi^ 
organic  matter.  It  is  not  a  desirable  practice  with  trees  ovei 
five  or  six  years  old. 

5.  A  large  proportion  of  the  phosphoric  acid  applied  in  the 
fertilizer  is  retained  in  the  upper  nine  inches  of  soil.  Prac-j 
tically  none  is  leached  out. 

6.  Much  of  the  potash  applied  in  the  water-soluble  form  is  re-j 
tained  by  the  soil. 

7.  Nitrogen,  both  in  the  organic  and  the  in-organic  form,  is 
lost  in  large  quantity  by  leaching  as  shown  by  the  lysemetel 
experiments  and  by  the  analyses  of  the  grove  soils.  Ther( 
was  a  slight  increase  of  nitrogen  in  all  plots  excepting  th^ 
clean  culture  and  the  unfertilized  ones. 


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